Role of a chemical/environmental engineer to manage solid wastes

/in /by

Ch. 14 Solid Waste – title

© 2010 Cengage Learning, Engineering

Chapter 14 Solid Waste

Environmental engineers design systems to manage solid

waste properly and consider the impacts or designs on the end-

of-life management options

 

 

Solid Waste • Solid waste generated in U.S.: 1.4 trillion lb of

garbage per day

• Refuse/Municipal solid waste is made up of:

o Garbage : which is food waste

o Rubbish : almost everything else in your

garbage can

o Trash : is larger items, such as old

refrigerators, tree limbs, mattresses, and

other bulky items, that are not commonly

collected with the household refuse

• A very important subcategory of solid waste,

called hazardous waste.

 

 

Solid Waste

The municipal solid waste problem can be

separated into three steps:

 

1. collection and transportation of household,

commercial, and industrial solid waste

 

2. recovery of useful fractions from this material

3. disposal of the residues into the environment.

 

 

Collection of refuge

In many locations in the United States and

other countries, solid waste from households and

commercial establishments is collected by trucks.

 

Sometimes these are open-bed trucks

that carry trash or bagged refuse.

 

These vehicles are called packers, trucks that

use hydraulic rams to compact the refuse to

reduce its volume and make it possible for the truck to carry larger loads (Figure 14.1)

 

 

Collection of refuge

Commercial and industrial collections are

facilitated by the use of containers (dumpsters or

roll-offs) that are either emptied into the truck by

using a hydraulic mechanism or carried by the

truck to the disposal site (Figure 14.2)

 

Vehicles for collecting separated materials,

such as newspaper, aluminum cans, and glass bottles, are also used (Figure 14.3)

 

 

Figure 14.1 pg 481

 

 

Collection of refuge

The entire operation is a study in inefficiency

and hazardous work conditions.

The safety record of solid waste collection

personnel is by far the worst of any group of

workers (three times as bad as coal miners, for

example).

Various modifications to this collection method

have been implemented to cut collection costs

and reduce accidents.

Compactors and garbage grinders in the

kitchen and semiautomated and fully automated

collection system can be used.

 

 

Figure 14.1 pg 481

 

 

Collection of refuge

Other alternate systems have been developed

for collecting refuse, one especially interesting

one being a system of underground pneumatic

pipes.

The pneumatic collection system at Disney

World in Florida has collection stations scattered

throughout the park that receive the refuse, and

the pneumatic pipes deliver the waste to a

central processing plant.

The selection of a proper route for collection

vehicles, known as route optimization,

can result in significant savings to the hauler.

 

 

Collection of refuge

Deposit your garbage at designated chutes

either on the street or in your building, which

transport the refuse (at high speeds!) through a

system of pressurized tubes hidden below the

streets.

 

Finally, it arrives at a central plant for

processing.

 

It’s cleaner, more efficient, and often less expensive than traditional truck collection,

 

 

Table 14.1 pg 483

© 2010 Cengage Learning, Engineering 14-11

 

 

© 2010 Cengage Learning, Engineering 14-12

 

 

14-13 Handbook of Solid Waste Management – Second Edition by George Tchobanoglous and Frank Kreith

 

 

Layout of Collection Routes

© 2010 Cengage Learning, Engineering 14-14

 

 

14-15

The effectiveness of the collection routes can be assessed by the amount of

route overlap. (a) Route layout with overlap shown by the dotted lines. (b)

Route layout without overlap.

Handbook of Solid Waste Management – Second Edition by George Tchobanoglous and Frank Kreith

 

 

 

Figure 14.8 pg 486

© 2010 Cengage Learning, Engineering 14-17

Tipping fee: Waste management fees for vehicles crossing solid waste management facility scales

 

 

Figure 14.9 pg 487

© 2010 Cengage Learning, Engineering 14-18

14.2 Generation of Refuse

 

 

Figure 14.11 pg 489

© 2010 Cengage Learning, Engineering 14-19

 

 

The public can exercise three alternate means for

getting rid of its unwanted material once it is generated—

reuse, recycling, and disposal

 

In reuse an individual either uses products again for the

same purpose or puts products to secondary, often

imaginative, use.

 

Recycling, or material recovery, on the other hand,

involves the collection of waste and subsequent

processing of that waste into new products—for example,

turning plastic food containers into park benches.

 

 A central processing facility is known as a material recovery facility, or MRF (pronounced “murf”)

Reuse and Recycling of Materials From Refuse

 

 

In both methods, reuse and recycling, the

primary goal is purity.

For example, the daily refuse from a city of

100,000 would contain perhaps 200 tons per day

of paper.

Secondary paper has sold for about $20/ton (but

it fluctuates greatly), so the income to the

community could be about $4,000 per day, or

about $1.5 million per year!

So why isn’t every community recovering the

paper from its refuse and selling it? The answer is

elementary— because processing the refuse to

recover the dirty paper costs more than producing paper from trees

Processing of Refuse

 

 

The obvious solution is to never dirty the paper

(and other materials that might have market value)

in the first place.

This requires the public to separate their waste,

a practice known as source separation.

Another option is to get rid of source separation

and let the MRF handle all the separation.

This reduces the public’s role and reduces

collection costs but increases the complexity of

and the processing costs at the MRF.

The most difficult operation in recycling is the identification and separation of plastics.

Processing of Refuse

 

 

Table 14.2 pg 493

© 2010 Cengage Learning, Engineering 14-23

Reuse and Recycling of Materials From Refuse

 

 

Figure 14.13 pg 494

 

 

One product that always has a market is energy.

 

Because refuse is about 80% combustible

material, it can be burned as is, or it can be

processed to produce a refuse-derived fuel (RDF).

 

A cross section of a typical waste-to-energy

(WTE) facility is shown in Figure 14.15.

 

The hot gases produced from the burning refuse are cooled with a bank of tubes filled with water.

Combustion of Refuge

 

 

As the gases are cooled, the water is heated,

producing low-pressure steam.

 

The steam can be used for heating and cooling

or for producing electricity in a turbine.

 

The cooled gases are then cleaned by pollution

control devices, such as electrostatic precipitators

and discharged through a stack.

Combustion of Refuge

 

 

14-27

 

 

Solid waste can be combusted as is and it can also

be processed in many ways before combustion

There might be confusion as to what exactly is

being burned.

The American Society for Testing and Materials

(ASTM) developed a scheme for classifying solid

waste destined for combustion:

RDF-1 unprocessed MSW

RDF-2 shredded MSW (but no separation of

materials)

RDF-3 organic fraction of shredded MSW (usually

produced in a MRF or from source-separated organics, such as newsprint)

Combustion of Refuge

 

 

RDF-4 organic waste produced by a MRF that

has been further shredded into a fine, almost

powder, form, sometimes called “fluff”

RDF-5 organic waste produced by a MRF that

has been densified by a pelletizer or a similar

device and that can often be fired with coal in

existing furnaces

RDF-6 organic fraction of the waste that has

been further processed into a liquid fuel, such as

oil

RDF-7 organic waste processed into a gaseous fuel.

Combustion of Refuge

 

 

Particular concern to many people is the

production of dioxin in waste combustion.

Dioxin is actually a family of organic compounds

called polychlorinated dibenzodioxins (PCDD).

Members of this family are characterized by a

triple-ring structure of two benzene rings

connected by a pair of oxygen atoms (Figure

14.17).

A related family of organic chemicals are the

polychlorinated dibenzofurans (PCDF), which

have a similar structure except that the two benzene rings are connected by only one oxygen.

Combustion of Refuge

 

 

Dioxin

© 2010 Cengage Learning, Engineering 14-31

 

 

All the PCDD and PCDF compounds (referred to

here as dioxins) have been found to be extremely

toxic to animals.

Neither PCDD nor PCDF compounds have

found any commercial use and are not

manufactured.

They do occur, however, as contaminants in

other organic chemicals.

Various forms of dioxins have been found in

pesticides and in various chlorinated organic chemicals (such as chlorophenols).

Combustion of Refuge

 

 

The only two realistic options for disposal are in

the oceans (or other large bodies of water) and on

land.

The former is presently forbidden by federal law

in the United States and is similarly illegal in most

other developed nations

Although the volume of the refuse is reduced by

over 90% in WTE facilities.

The remaining 10% still has to be disposed of

somehow, along with the materials that cannot be incinerated, such as old refrigerators.

Sanitary Landfills

 

 

A landfill is, therefore, necessary even if the

refuse is combusted, and a WTE plant is, therefore,

not an ultimate disposal facility.

The placement of solid waste on land is called a

dump in the United States and a tip in Great Britain

(as in “tipping”).

The dump is by far the least expensive means of

solid waste disposal and thus was the original

method of choice for almost all inland communities.

The operation of a dump is simple and involves

nothing more than making sure that the trucks empty at the proper spot.

Sanitary Landfills

 

 

Rodents, odor, air pollution, and insects at the

dump, however, can result in serious public health

and aesthetic problems, and alternate methods for

disposal are necessary.

Larger communities can afford to use an

incinerator for volume reduction.

But smaller towns cannot afford such capital

investment, so this has led to the development of

the sanitary landfill.

The sanitary landfill differs markedly from open

dumps in that the latter are simply places to dump

wastes while sanitary landfills are engineered

operations, designed and operated according to accepted standards.

Sanitary Landfills

 

 

The basic principle of a landfill operation is to

prepare a site with liners to deter pollution of

groundwater, deposit the refuse in the pit,

compact it with specially built heavy machinery

with huge steel wheels, and cover the material at

the conclusion of each day’s operation (Figure

14.18).

 

Developing a proper landfill requires planning and engineering design skills.

Sanitary Landfills

 

 

Figure 14.18 pg 502

© 2010 Cengage Learning, Engineering 14-37

 

 

Table 14.3 pg 503

© 2010 Cengage Learning, Engineering 14-38

 

 

Imagine a town where 10,000 households each

fill up one 80-gallon container of refuse per week.

To what density would a 20-cubic-yard packer

truck have to compact the refuse to be able to

collect all the households during one trip?

[Mass IN] = [Mass OUT]

VLCL = VPCP where V and C are the volume and density of the

refuse and the subscripts L and P denote

loose and packed refuse. Assume that the density in the cans is 200 lb/yd3 (Table 14.3).

Example 14.2

 

 

[(10,000 households)(80 gal/household)(0.00495

yd3/gal)] × [200 lb/yd3] = (20 yd3)CP

CP = 39,600 lb/yd 3(!)

 

Clearly impossible. Obviously, more than one truck and/or more than one trip is required.

Example 14.2

 

 

An added complication in the calculation of

landfill volume is the need for the daily cover,

which may be removable (such as a plastic ‘tarp’)

and not use any of the volume or may not be

removable (such as dirt).

The more permanent cover material (e.g., dirt)

that is placed on the refuse, the less volume there

is available for the refuse itself, so the shorter

the life of the landfill.

Commonly, engineers estimate that the volume

occupied by cover dirt is one-fourth the total landfill volume.

Sanitary Landfills

 

 

Sanitary landfills are not inert.

The buried organic material decomposes,

first aerobically and then anaerobically.

The anaerobic degradation produces various

gases, such as methane and carbon dioxide, and

liquids (known as leachate) that have extremely

high pollution capacity when they enter the

groundwater.

Liners made of either impervious clay or

synthetic materials, such as plastic, are used to

try to prevent the movement of leachate into the groundwater.

Sanitary Landfills

 

 

Figure 14.19 pg 504

© 2010 Cengage Learning, Engineering 14-43

 

 

Synthetic landfill liners are useful in capturing

most of the leachate, but they cannot be perfect.

No landfill is sufficiently tight that groundwater

contamination by leachate is totally avoided.

Wells have to be drilled around the landfill to

check for groundwater contamination from leaking

liners, and if such contamination is found,

remedial action is necessary.

The use of plastic liners substantially increased

the cost of landfills to the point where a modern

landfill costs nearly as much per ton of refuse as a WTE plant

Sanitary Landfills

 

 

Modern landfills also require the gases to be

collected and either burned or vented to the

atmosphere.

The gases are about 50% carbon dioxide and

50% methane, both of which are greenhouse

gases.

In the past, when gas control in landfills was

not practiced, the gases were known to cause

problems with odor, soil productivity, and

even explosions.

Now the larger landfills use the gases for

running turbines to produce electricity to sell to

the power company. Smaller landfills simply burn the gases at flares.

Sanitary Landfills

 

 

Reducing the generation of Refuge: Source Reduction Pages 505 – 509

 

 

The EPA developed a national strategy

for the management of solid waste called

“integrated solid waste management”

(ISWM).

 

The intent of this plan is to assist local

communities in their decision making by

encouraging strategies that are the most

environmentally acceptable but providing

flexibility to manage wastes efficiently.

Integrated Solid Waste Management

 

 

It is based on the solid waste management

hierarchy, with the most-to-least-desirable solid

waste management strategies being

• source reduction

• recycling

• combustion

• landfilling

Read Pages 509-511

Integrated Solid Waste Management

 

 

Figure 14.24 pg 514

© 2010 Cengage Learning, Engineering 14-49

Simulate In Comsol Or Matlab And Get The Results.

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Available online at www.sciencedirect.comAvailable online at www.sciencedirect.com

ScienceDirect Energy Procedia 00 (2017) 000–000

www.elsevier.com/locate/procedia

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.

The 15th International Symposium on District Heating and Cooling

Assessing the feasibility of using the heat demand-outdoor temperature function for a long-term district heat demand forecast

I. Andrića,b,c*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc

aIN+ Center for Innovation, Technology and Policy Research – Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal bVeolia Recherche & Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France

cDépartement Systèmes Énergétiques et Environnement – IMT Atlantique, 4 rue Alfred Kastler, 44300 Nantes, France

Abstract

District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand – outdoor temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.

© 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.

Keywords: Heat demand; Forecast; Climate change

Energy Procedia 138 (2017) 518–523

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 2017 International Conference on Alternative Energy in Developing Countries and Emerging Economies. 10.1016/j.egypro.2017.10.238

10.1016/j.egypro.2017.10.238 1876-6102

© 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 2017 International Conference on Alternative Energy in Developing Countries and Emerging Economies.

 

Available online at www.sciencedirect.com

ScienceDirect Energy Procedia 00 (2017) 000–000

www.elsevier.com/locate/procedia

 

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Organizing Committee of 2017 AEDCEE.

2017 International Conference on Alternative Energy in Developing Countries and Emerging Economies 2017 AEDCEE, 25‐26 May 2017, Bangkok, Thailand

Computational Fluid Dynamics Model of CO2 Capture in Fluidized Bed Reactors: Operating Parameter Optimization

Chattan Sakaunnapaporna, Pornpote Piumsomboona,b, Benjapon Chalermsinsuwana,b,* aFuels Research Center, Department of Chemical Technology, Faculty of Science, Chulalongkorn University,

254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand bCenter of Excellence on Petrochemical and Materials Technology, Chulalongkorn University,

254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand

Abstract

Alternative energy is one of the methods for decreasing fossil fuel consumption. However, conventional fossil fuel process improvement is also considerably interesting issue due to the fact that adjusting existing process is easier and cheaper comparing to the development of the process compatible with the alternative energy. At present, the global warming and climate change phenomenon cause the increasing of average earth temperature. The CO2 emission to the atmosphere is mainly produced by fossil fuel combustion from power industry. This is because the CO2 has high heat capacity. Therefore, in order to use the conventional fossil fuel process efficiently, CO2 should be eliminated from the flue gas before releasing it to the environment. Currently, there are many methods that use to capture CO2 such as using circulating fluidized bed riser with solid sorbent. The advantages of circulating fluidized bed riser are uniform solid particle and temperature distributions, high contacting area between gas-solid particle and suitable for continuous operation. In this study, the effect of operating parameters on CO2 capture in circulating fluidized bed riser with solid sorbent is investigated using 2D computational fluid dynamics model. The basic simulation step has to find the suitable computational mesh cells or grid independency test (5,000, 10,000, 15,000 and 20,000 cells) and compare the simulation result with the real experimental result. According to the simulation results, the suitable mesh cell is 10,000 cells and the obtained result is matched with the experimental results. Then, the effect of operating parameters on the CO2 capture conversion is optimized. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Organizing Committee of 2017 AEDCEE.

Keywords: Circulating fluidized bed reactor, CO2 capture; Computational fluid dynamics,Optimization; 2k factorial design.

 

* Corresponding author. Tel.: +662-218-7682; fax: +662-255-5831.

E-mail address: benjapon.c@chula.ac.th

 

Available online at www.sciencedirect.com

ScienceDirect Energy Procedia 00 (2017) 000–000

www.elsevier.com/locate/procedia

 

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Organizing Committee of 2017 AEDCEE.

2017 International Conference on Alternative Energy in Developing Countries and Emerging Economies 2017 AEDCEE, 25‐26 May 2017, Bangkok, Thailand

Computational Fluid Dynamics Model of CO2 Capture in Fluidized Bed Reactors: Operating Parameter Optimization

Chattan Sakaunnapaporna, Pornpote Piumsomboona,b, Benjapon Chalermsinsuwana,b,* aFuels Research Center, Department of Chemical Technology, Faculty of Science, Chulalongkorn University,

254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand bCenter of Excellence on Petrochemical and Materials Technology, Chulalongkorn University,

254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand

Abstract

Alternative energy is one of the methods for decreasing fossil fuel consumption. However, conventional fossil fuel process improvement is also considerably interesting issue due to the fact that adjusting existing process is easier and cheaper comparing to the development of the process compatible with the alternative energy. At present, the global warming and climate change phenomenon cause the increasing of average earth temperature. The CO2 emission to the atmosphere is mainly produced by fossil fuel combustion from power industry. This is because the CO2 has high heat capacity. Therefore, in order to use the conventional fossil fuel process efficiently, CO2 should be eliminated from the flue gas before releasing it to the environment. Currently, there are many methods that use to capture CO2 such as using circulating fluidized bed riser with solid sorbent. The advantages of circulating fluidized bed riser are uniform solid particle and temperature distributions, high contacting area between gas-solid particle and suitable for continuous operation. In this study, the effect of operating parameters on CO2 capture in circulating fluidized bed riser with solid sorbent is investigated using 2D computational fluid dynamics model. The basic simulation step has to find the suitable computational mesh cells or grid independency test (5,000, 10,000, 15,000 and 20,000 cells) and compare the simulation result with the real experimental result. According to the simulation results, the suitable mesh cell is 10,000 cells and the obtained result is matched with the experimental results. Then, the effect of operating parameters on the CO2 capture conversion is optimized. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Organizing Committee of 2017 AEDCEE.

Keywords: Circulating fluidized bed reactor, CO2 capture; Computational fluid dynamics,Optimization; 2k factorial design.

 

* Corresponding author. Tel.: +662-218-7682; fax: +662-255-5831.

E-mail address: benjapon.c@chula.ac.th

2 Author name / Energy Procedia 00 (2017) 000–000

Nomenclature

k number of considered parameter

1. Introduction

Nowadays, the emission of carbon dioxide (CO2) from chemical industry is a major cause of the global warming because CO2 can absorb and maintain the heat which then has an impact on climate change. Currently, alternative energy is one of the methods for decreasing fossil fuel consumption such as solar energy and wind energy. It can decrease air pollution which is primary cause of the global warming, but the investment of equipment in building alternative energy plant is very expensive. Thus, conventional fossil fuel process improvement is also considerably interesting issue due to the fact that adjusting existing process is easier and cheaper comparing to the development of the process compatible with the alternative energy. There are many methods that use to capture CO2 such as using circulating fluidized bed riser with alkali-based solid sorbent. Alkali metal carbonates such as Na2CO3 and K2CO3 react with CO2 and H2O and transform to alkali metal hydrogen carbonates after CO2 adsorption [1]. In fluidized bed reactor, the solid flow pattern is important quantitatively due to difference solid flow pattern will affect the rate heat and mass transfers.

There are many researches that study the effect of operating parameter on CO2 adsorption in circulating fluidized bed riser. Wang et al. [2] researched about CO2 capture using potassium-based sorbents in circulating fluidized bed reactor at different inlet gas velocities using simulation method by considering effect of particle clusters. According to their results, the simulation with particle cluster effect predicted the system hydrodynamics similar to the experimental result more than the simulation without particle cluster effect. Yi et al. [3] studied the effect of operating parameters, gas inlet velocity, solid circulation rate and water content in feed gas, on CO2 removal percentage in circulating fluidized bed reactor by using K2CO3 solid sorbent. As a result, the increase of the overall CO2 removal is owing to the increasing solid circulation rate and water vapor content and the decreasing gas velocity. Zhao et al. [4] studied the effect of amount of K2CO3 on CO2 sorption capacity. The CO2 sorption capacity increased when increasing the amount of K2CO3. Yafei et al. [5] investigated the CO2 capture performance of some wood materials by using fluidized bed reactor. The component of employed wood materials was investigated by XRD which showed high K2CO3 component. According the results, the CO2 capture capacity increased when the reaction temperature decreased (60 to 100oC) and mole ratio between water and CO2 increased. Apart from the experimental method, the simulation method was used to study the CO2 capture processes. Emadoddin et al. [6] simulated CO2 sorption in circulating fluidized bed using deactivation kinetic model and compared the results with experimental information and other chemical reaction models. According the results, differential pressure from simulation result was similar to experimental result [3]. In addition, the deactivation kinetic reaction model predicted the CO2 removal percentage accurately more than the other chemical reaction model. However, the systematically study of the effect of operating parameters on the CO2 removal percentage is still lacking in the literature. Most of the studies were considered the experiment using one factor at a time methodology. With this methodology, the interaction effect between operating parameters cannot be obtained.

The main objective in this study is therefore to investigate the effect of the different inlet gas velocities and the solid circulation rate on the CO2 conversion using two-dimensional computational fluid dynamics model. The numerical model is comparing its correctness with the literature experimental data by Yi et al. [3]. In this study, the response surface via 2k factorial statistical experimental design (with literature base case condition) was found for determining the operating parameter optimization on the CO2 conversion in circulating fluidized bed reactor.

2. Methodology

2.1 Computational model

In this study, the circulating fluidized bed riser was constructed by using computer–aided design program, DESIGN MODULER and was simulated by using computational fluid dynamics simulation program, ANSYS FLUENT. The model in two-dimensional Cartesian coordinate system which consisting of 5,000, 10,000, 15,000, 20,000 mesh cells and 80 s flow time was used. The gas and solid particles entered to the circulating fluidized bed

 

 

Chattan Sakaunnapaporn et al. / Energy Procedia 138 (2017) 518–523 519

 

Available online at www.sciencedirect.com

ScienceDirect Energy Procedia 00 (2017) 000–000

www.elsevier.com/locate/procedia

 

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Organizing Committee of 2017 AEDCEE.

2017 International Conference on Alternative Energy in Developing Countries and Emerging Economies 2017 AEDCEE, 25‐26 May 2017, Bangkok, Thailand

Computational Fluid Dynamics Model of CO2 Capture in Fluidized Bed Reactors: Operating Parameter Optimization

Chattan Sakaunnapaporna, Pornpote Piumsomboona,b, Benjapon Chalermsinsuwana,b,* aFuels Research Center, Department of Chemical Technology, Faculty of Science, Chulalongkorn University,

254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand bCenter of Excellence on Petrochemical and Materials Technology, Chulalongkorn University,

254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand

Abstract

Alternative energy is one of the methods for decreasing fossil fuel consumption. However, conventional fossil fuel process improvement is also considerably interesting issue due to the fact that adjusting existing process is easier and cheaper comparing to the development of the process compatible with the alternative energy. At present, the global warming and climate change phenomenon cause the increasing of average earth temperature. The CO2 emission to the atmosphere is mainly produced by fossil fuel combustion from power industry. This is because the CO2 has high heat capacity. Therefore, in order to use the conventional fossil fuel process efficiently, CO2 should be eliminated from the flue gas before releasing it to the environment. Currently, there are many methods that use to capture CO2 such as using circulating fluidized bed riser with solid sorbent. The advantages of circulating fluidized bed riser are uniform solid particle and temperature distributions, high contacting area between gas-solid particle and suitable for continuous operation. In this study, the effect of operating parameters on CO2 capture in circulating fluidized bed riser with solid sorbent is investigated using 2D computational fluid dynamics model. The basic simulation step has to find the suitable computational mesh cells or grid independency test (5,000, 10,000, 15,000 and 20,000 cells) and compare the simulation result with the real experimental result. According to the simulation results, the suitable mesh cell is 10,000 cells and the obtained result is matched with the experimental results. Then, the effect of operating parameters on the CO2 capture conversion is optimized. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Organizing Committee of 2017 AEDCEE.

Keywords: Circulating fluidized bed reactor, CO2 capture; Computational fluid dynamics,Optimization; 2k factorial design.

 

* Corresponding author. Tel.: +662-218-7682; fax: +662-255-5831.

E-mail address: benjapon.c@chula.ac.th

 

Available online at www.sciencedirect.com

ScienceDirect Energy Procedia 00 (2017) 000–000

www.elsevier.com/locate/procedia

 

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Organizing Committee of 2017 AEDCEE.

2017 International Conference on Alternative Energy in Developing Countries and Emerging Economies 2017 AEDCEE, 25‐26 May 2017, Bangkok, Thailand

Computational Fluid Dynamics Model of CO2 Capture in Fluidized Bed Reactors: Operating Parameter Optimization

Chattan Sakaunnapaporna, Pornpote Piumsomboona,b, Benjapon Chalermsinsuwana,b,* aFuels Research Center, Department of Chemical Technology, Faculty of Science, Chulalongkorn University,

254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand bCenter of Excellence on Petrochemical and Materials Technology, Chulalongkorn University,

254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand

Abstract

Alternative energy is one of the methods for decreasing fossil fuel consumption. However, conventional fossil fuel process improvement is also considerably interesting issue due to the fact that adjusting existing process is easier and cheaper comparing to the development of the process compatible with the alternative energy. At present, the global warming and climate change phenomenon cause the increasing of average earth temperature. The CO2 emission to the atmosphere is mainly produced by fossil fuel combustion from power industry. This is because the CO2 has high heat capacity. Therefore, in order to use the conventional fossil fuel process efficiently, CO2 should be eliminated from the flue gas before releasing it to the environment. Currently, there are many methods that use to capture CO2 such as using circulating fluidized bed riser with solid sorbent. The advantages of circulating fluidized bed riser are uniform solid particle and temperature distributions, high contacting area between gas-solid particle and suitable for continuous operation. In this study, the effect of operating parameters on CO2 capture in circulating fluidized bed riser with solid sorbent is investigated using 2D computational fluid dynamics model. The basic simulation step has to find the suitable computational mesh cells or grid independency test (5,000, 10,000, 15,000 and 20,000 cells) and compare the simulation result with the real experimental result. According to the simulation results, the suitable mesh cell is 10,000 cells and the obtained result is matched with the experimental results. Then, the effect of operating parameters on the CO2 capture conversion is optimized. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Organizing Committee of 2017 AEDCEE.

Keywords: Circulating fluidized bed reactor, CO2 capture; Computational fluid dynamics,Optimization; 2k factorial design.

 

* Corresponding author. Tel.: +662-218-7682; fax: +662-255-5831.

E-mail address: benjapon.c@chula.ac.th

2 Author name / Energy Procedia 00 (2017) 000–000

Nomenclature

k number of considered parameter

1. Introduction

Nowadays, the emission of carbon dioxide (CO2) from chemical industry is a major cause of the global warming because CO2 can absorb and maintain the heat which then has an impact on climate change. Currently, alternative energy is one of the methods for decreasing fossil fuel consumption such as solar energy and wind energy. It can decrease air pollution which is primary cause of the global warming, but the investment of equipment in building alternative energy plant is very expensive. Thus, conventional fossil fuel process improvement is also considerably interesting issue due to the fact that adjusting existing process is easier and cheaper comparing to the development of the process compatible with the alternative energy. There are many methods that use to capture CO2 such as using circulating fluidized bed riser with alkali-based solid sorbent. Alkali metal carbonates such as Na2CO3 and K2CO3 react with CO2 and H2O and transform to alkali metal hydrogen carbonates after CO2 adsorption [1]. In fluidized bed reactor, the solid flow pattern is important quantitatively due to difference solid flow pattern will affect the rate heat and mass transfers.

There are many researches that study the effect of operating parameter on CO2 adsorption in circulating fluidized bed riser. Wang et al. [2] researched about CO2 capture using potassium-based sorbents in circulating fluidized bed reactor at different inlet gas velocities using simulation method by considering effect of particle clusters. According to their results, the simulation with particle cluster effect predicted the system hydrodynamics similar to the experimental result more than the simulation without particle cluster effect. Yi et al. [3] studied the effect of operating parameters, gas inlet velocity, solid circulation rate and water content in feed gas, on CO2 removal percentage in circulating fluidized bed reactor by using K2CO3 solid sorbent. As a result, the increase of the overall CO2 removal is owing to the increasing solid circulation rate and water vapor content and the decreasing gas velocity. Zhao et al. [4] studied the effect of amount of K2CO3 on CO2 sorption capacity. The CO2 sorption capacity increased when increasing the amount of K2CO3. Yafei et al. [5] investigated the CO2 capture performance of some wood materials by using fluidized bed reactor. The component of employed wood materials was investigated by XRD which showed high K2CO3 component. According the results, the CO2 capture capacity increased when the reaction temperature decreased (60 to 100oC) and mole ratio between water and CO2 increased. Apart from the experimental method, the simulation method was used to study the CO2 capture processes. Emadoddin et al. [6] simulated CO2 sorption in circulating fluidized bed using deactivation kinetic model and compared the results with experimental information and other chemical reaction models. According the results, differential pressure from simulation result was similar to experimental result [3]. In addition, the deactivation kinetic reaction model predicted the CO2 removal percentage accurately more than the other chemical reaction model. However, the systematically study of the effect of operating parameters on the CO2 removal percentage is still lacking in the literature. Most of the studies were considered the experiment using one factor at a time methodology. With this methodology, the interaction effect between operating parameters cannot be obtained.

The main objective in this study is therefore to investigate the effect of the different inlet gas velocities and the solid circulation rate on the CO2 conversion using two-dimensional computational fluid dynamics model. The numerical model is comparing its correctness with the literature experimental data by Yi et al. [3]. In this study, the response surface via 2k factorial statistical experimental design (with literature base case condition) was found for determining the operating parameter optimization on the CO2 conversion in circulating fluidized bed reactor.

2. Methodology

2.1 Computational model

In this study, the circulating fluidized bed riser was constructed by using computer–aided design program, DESIGN MODULER and was simulated by using computational fluid dynamics simulation program, ANSYS FLUENT. The model in two-dimensional Cartesian coordinate system which consisting of 5,000, 10,000, 15,000, 20,000 mesh cells and 80 s flow time was used. The gas and solid particles entered to the circulating fluidized bed

 

 

520 Chattan Sakaunnapaporn et al. / Energy Procedia 138 (2017) 518–523 Author name / Energy Procedia 00 (2017) 000–000 3

riser and entrained out the circulating fluidized bed riser at the bottom and top sections, respectively. The simplified schematic drawing of the circulating fluidized bed riser is shown in Fig. 1. The mixing zone was set about 0.6 m height and the fast fluidization zone was set about 5.6 m height.

 

 

Fig. 1. The simplified schematic drawing of the circulating fluidized bed riser.

2.2 Mathematical model

The mathematical model that used in this study consisted of four conservation equations, which were mass, momentum, energy and fluctuating kinetic energy (granular temperature) conservation equations, and other related constitutive equations similar to the ones formulated by Chalermsinsuwan et al. [7]. For the constitutive equations, the kinetic theory of granular flow concept was used to explain the solid particle flow behaviour. In this study, three reaction kinetic models for simulation the CO2 adsorption that were the Homogenous model [8], the Deactivation model [9] and the Equilibrium model [10] were simulated and compared the result with experimental information by Yi et al. [3].

2.3 Boundary and initial conditions

In this study, the gas phase consisted of CO2, H2O and N2 that had mass fraction of 0.10, 0.15 and 0.75, respectively. The solid particles were potassium carbonate (K2CO3) particles, with average diameter of 98 microns and bulk density of 1,100 kg/m3. For the boundary condition, no slip condition was used for gas phase at the wall and partial slip condition was used for solid particle phase. For the initial conditions, there were no gas and solid phases in the circulating fluidized bed riser. The operating gravitational force was –9.81 m/s2 in y direction and the operating pressure was set equal to 101,325 Pa. To analyse the system hydrodynamics and the CO2 conversion, the 2k factorial statistical experimental design (with literature base case condition) was used to determine the effect of the inlet gas velocity and the solid circulation rate on the CO2 conversion as summarized in Table 1.

Table1. The statistical experimental design cases.

Case Inlet gas velocity (m/s) Solid circulation rate (kg/m2s) CO2 removal percentage (-)

0 (base case) 1 21 58.46

1 1 10 32.35

2 1 30 70.38

3 3 10 0.65

4 3 30 4.23

4 Author name / Energy Procedia 00 (2017) 000–000

3. Results and discussion

3.1 Grid independency test and experimental validation The grid independency test and the comparison of the simulation result with literature experimental results are

important steps for performing computational fluid dynamics simulation. This study results were averaged after the system reached quasi steady state condition (simulation time of 60-80 s). Fig.2 (a) shows the differential pressure at four elevation heights (at elevation heights of 0.52 m, 2.27 m, 4.07 m, 5.87 m, respectively) comparing between simulation result and the experimental result. It was found that simulated differential pressure results were consistent with the experimental result. The selected suitable mesh cell should be the lowest mesh cells for saving time but still could predict the obtained result accurately. Fig.2 (b) illustrates the averaged CO2 mass fraction with different mesh cells and chemical reaction kinetic models. As a result, the suitable mesh cells was 10,000 cells because the predicted average CO2 mass fraction was similar to the ones with 15,000 and 20,000 cells and similar to experimental result of Yi et al. [3] with the outlet CO2 mass fraction of 0.042. All the reaction kinetic model, homogenous model, deactivation model and equilibrium model, was well predicted the CO2 capture process in circulating fluidized bed riser. However, due to the experimental data comparison and the easier of the methodology, the homogeneous model was then used in the subsequence simulation. From the validation of the results, this confirms the correctness of the employed computational fluid dynamics model.

(a) (b)

Fig. 2. (a) Differential pressure at differential elevation heights and (b) averaged CO2 mass fraction at different riser heights.

3.2 Solid volume fraction and CO2 mass fraction

The interaction between solid particle phase and gas phase in circulating fluidized bed riser has an important effect on the CO2 removal percentage inside the system. This is because the K2CO3 captures CO2 with the chemical reaction: K2CO3(s) + CO2(g) + H2O(g)  2KHCO3(s). Therefore, the contacting between solid particle phase and gas phase is crucial for occurring the adsorption. The contour of solid volume fraction for base case operating condition, inlet gas velocity of 1 m/s and solid circulation rate of 21 kg/m2s, is shown in Fig. 3 (a). The color scale bar represents the quantity of the solid volume fraction which red color is highest value and blue color is lowest value. According to the results, the mixing zone had higher solid volume fraction than the fast fluidization zone because the mixing zone had larger system diameter. The large area will have an effect on the reduction of gas and solid particle velocities. In addition, the solid particle moved down to the mixing zone by the energy loss from wall effect. These obtained phenomena are consistent with the results in Fig. 3(b). Fig. 3(b) depicts the contour of CO2 mass fraction for base case operating condition. The meaning of color scale bar is similar to the ones for solid volume fraction. The CO2 mass fraction was high and low at the bottom zone and top zone, respectively, because the CO2 reacted with K2CO3.

 

 

Chattan Sakaunnapaporn et al. / Energy Procedia 138 (2017) 518–523 521 Author name / Energy Procedia 00 (2017) 000–000 3

riser and entrained out the circulating fluidized bed riser at the bottom and top sections, respectively. The simplified schematic drawing of the circulating fluidized bed riser is shown in Fig. 1. The mixing zone was set about 0.6 m height and the fast fluidization zone was set about 5.6 m height.

 

 

Fig. 1. The simplified schematic drawing of the circulating fluidized bed riser.

2.2 Mathematical model

The mathematical model that used in this study consisted of four conservation equations, which were mass, momentum, energy and fluctuating kinetic energy (granular temperature) conservation equations, and other related constitutive equations similar to the ones formulated by Chalermsinsuwan et al. [7]. For the constitutive equations, the kinetic theory of granular flow concept was used to explain the solid particle flow behaviour. In this study, three reaction kinetic models for simulation the CO2 adsorption that were the Homogenous model [8], the Deactivation model [9] and the Equilibrium model [10] were simulated and compared the result with experimental information by Yi et al. [3].

2.3 Boundary and initial conditions

In this study, the gas phase consisted of CO2, H2O and N2 that had mass fraction of 0.10, 0.15 and 0.75, respectively. The solid particles were potassium carbonate (K2CO3) particles, with average diameter of 98 microns and bulk density of 1,100 kg/m3. For the boundary condition, no slip condition was used for gas phase at the wall and partial slip condition was used for solid particle phase. For the initial conditions, there were no gas and solid phases in the circulating fluidized bed riser. The operating gravitational force was –9.81 m/s2 in y direction and the operating pressure was set equal to 101,325 Pa. To analyse the system hydrodynamics and the CO2 conversion, the 2k factorial statistical experimental design (with literature base case condition) was used to determine the effect of the inlet gas velocity and the solid circulation rate on the CO2 conversion as summarized in Table 1.

Table1. The statistical experimental design cases.

Case Inlet gas velocity (m/s) Solid circulation rate (kg/m2s) CO2 removal percentage (-)

0 (base case) 1 21 58.46

1 1 10 32.35

2 1 30 70.38

3 3 10 0.65

4 3 30 4.23

4 Author name / Energy Procedia 00 (2017) 000–000

3. Results and discussion

3.1 Grid independency test and experimental validation The grid independency test and the comparison of the simulation result with literature experimental results are

important steps for performing computational fluid dynamics simulation. This study results were averaged after the system reached quasi steady state condition (simulation time of 60-80 s). Fig.2 (a) shows the differential pressure at four elevation heights (at elevation heights of 0.52 m, 2.27 m, 4.07 m, 5.87 m, respectively) comparing between simulation result and the experimental result. It was found that simulated differential pressure results were consistent with the experimental result. The selected suitable mesh cell should be the lowest mesh cells for saving time but still could predict the obtained result accurately. Fig.2 (b) illustrates the averaged CO2 mass fraction with different mesh cells and chemical reaction kinetic models. As a result, the suitable mesh cells was 10,000 cells because the predicted average CO2 mass fraction was similar to the ones with 15,000 and 20,000 cells and similar to experimental result of Yi et al. [3] with the outlet CO2 mass fraction of 0.042. All the reaction kinetic model, homogenous model, deactivation model and equilibrium model, was well predicted the CO2 capture process in circulating fluidized bed riser. However, due to the experimental data comparison and the easier of the methodology, the homogeneous model was then used in the subsequence simulation. From the validation of the results, this confirms the correctness of the employed computational fluid dynamics model.

(a) (b)

Fig. 2. (a) Differential pressure at differential elevation heights and (b) averaged CO2 mass fraction at different riser heights.

3.2 Solid volume fraction and CO2 mass fraction

The interaction between solid particle phase and gas phase in circulating fluidized bed riser has an important effect on the CO2 removal percentage inside the system. This is because the K2CO3 captures CO2 with the chemical reaction: K2CO3(s) + CO2(g) + H2O(g)  2KHCO3(s). Therefore, the contacting between solid particle phase and gas phase is crucial for occurring the adsorption. The contour of solid volume fraction for base case operating condition, inlet gas velocity of 1 m/s and solid circulation rate of 21 kg/m2s, is shown in Fig. 3 (a). The color scale bar represents the quantity of the solid volume fraction which red color is highest value and blue color is lowest value. According to the results, the mixing zone had higher solid volume fraction than the fast fluidization zone because the mixing zone had larger system diameter. The large area will have an effect on the reduction of gas and solid particle velocities. In addition, the solid particle moved down to the mixing zone by the energy loss from wall effect. These obtained phenomena are consistent with the results in Fig. 3(b). Fig. 3(b) depicts the contour of CO2 mass fraction for base case operating condition. The meaning of color scale bar is similar to the ones for solid volume fraction. The CO2 mass fraction was high and low at the bottom zone and top zone, respectively, because the CO2 reacted with K2CO3.

 

 

522 Chattan Sakaunnapaporn et al. / Energy Procedia 138 (2017) 518–523 Author name / Energy Procedia 00 (2017) 000–000 5

(a) (b)

Fig. 3. (a) Contour of solid volume fraction and (b) contour of CO2 mass fraction (at three different quasi-steady state simulation times).

3.3 Analysis of variance for the statistical experimental design

The 2k factorial statistical experimental design methodology (with literature base case condition) is useful in performing the experiment due to its many advantages. It gives the smallest number of runs for k factors. However, the full parameter analysis can still be obtained. With this methodology, the two levels of each factor represent the low and high values. In this study, the statistical experimental design had the inlet gas velocity as a first factor and solid circulation rate as a second factor. The response variable was CO2 removal percentage at the outlet of circulating fluidized bed riser. The analysis of variance result for the statistical experimental design is summarized in Table 2. The p–value was used for the statistical testing. If the p–value is lower than 0.05, the factor significantly affects the interested response. From the results, it can be summarized that inlet gas velocity had significantly affected on the CO2 removal percentage. In addition, it was found that effect of the solid sorbent loading and the interaction between inlet gas velocity and solid sorbent loading did not have an effect on the CO2 conversion significantly. Fig. 4 illustrates the main effect plot of the inlet gas velocity and the solid circulation rate on the CO2 removal percentage. When increasing the inlet gas velocity and the solid circulation rate, the CO2 removal percentage was lower and higher, respectively. The high gas velocity will decrease the system residence time and reduce the contacting between gas and solid particles. The high solid circulation rate will increase the quantity of reactant material of the adsorption inside the circulating fluidized bed riser.

Fig. 5 shows the response surface of CO2 removal percentage with the changing of inlet gas velocity and the solid circulation rate. The response surface can be used to choose the operating condition with desired outcome or response. For this circulating fluidized bed riser, the highest CO2 removal percentage is preferred. Therefore, the low inlet gas velocity and high solid circulation rate is needed to operate the system to obtain the high CO2 removal percentage.

Table 2. The analysis of variance result for the statistical experimental design.

Source Sum of DF Mean F Prob > F Squares Square Value

A 3076.67 1 3076.67 171.75 0.05 B 440.82 1 440.82 24.61 0.13

AB 303.33 1 303.33 16.93 0.15 Residual 17.91 1 17.91 Cor Total 3920.26 4

 

6 Author name / Energy Procedia 00 (2017) 000–000

 

Fig. 4. This study main effect plot. Fig. 5. This study response surface contour.

4. Conclusion

In this study, the computational fluid dynamics model which had 10,000 mesh cells and three reaction kinetic models was accurately used to predict CO2 removal percentage and system hydrodynamics of circulating fluidized bed riser comparing with the experimental results of Yi et al. [3]. From the 2k factorial statistical experimental design (with literature base case condition), the increasing of inlet gas velocity and solid sorbent circulation rate gave lower and higher CO2 removal percentage, respectively. In addition, the analysis concluded the significant effect of inlet gas velocity on the CO2 removal. The low inlet gas velocity and high solid circulation rate is needed to operate the system to obtain the high CO2 removal percentage.

Acknowledgements

This study was financially supported by the Scholarship from the Graduate School, Chulalongkorn University to commemorate the 72nd anniversary of his Majesty King Bhumibol Aduladej, the 90th Anniversary of Chulalongkorn University Fund, the Graduate School Thesis Grant, the National Research Council of Thailand, the Thailand Research Fund for fiscal year 2016–2019 (RSA5980052), and Ratchadapisek Sompoch Endowment Fund (2016), Chulalongkorn University (CU-59-003-IC).

References

[1] Abanades JC, Antrony EJ, Wang, J, Oakey JE. Fluidized-bed combustion system integration CO2 capture with CaO. Environ Sci Technol 2005; 39:2861–2866. [2] Wang S, Wang Q, Chen J, Liu G, Lu H, Sun L. Assessment of CO2 capture using potassium-based sorbents in circulating fluidized bed reactor by multiscale modeling. Fuel 2016; 164:66–72. [3] Yi CK, Jo SJ, Seo Y, Lee JB, Ryu CK. Continuous operation of the potassium-based dry sorbent CO2 capture process with two fluidized-bed reactors. Int J Greenhouse Gas Control 2007; 1:31-36. [4] Zhao C, Chen X, Zhao C, Wu Y, Dong W. K2CO3/Al2O3 for capturing CO2 in flue gas from power plants. Part 3: CO2 capture behaviors of K2CO3/Al2O3 in a bubbling fluidized-bed reactor. Energy Fuels 2012; 26:3062–3068. [5] Yafei G, Chuanwen Z, Xiaoping C, Changhai L. CO2 capture and sorbent regeneration performances of some wood ash materials. Appl Energ 2015; 137:26–36. [6] Emadoddin A, Hamid A. CFD simulation of CO2 sorption in a circulating fluidized bed using deactivation kinetic model. 10th International Conference on Circulating Fluidized Beds and Fluidization Technology – CFB-10, US, May 1 – May 5, 2011. [7] Chalermsinsuwan B, Piumsomboon P, Gidaspow D. Kinetic theory based computation of PSRI riser: Part I–Estimate of mass transfer coefficient. Chem Eng Sci 2009; 64:1195–1211. [8] Garg R, Shahnam M, Huckaby ED. Continuum simulations of CO2 capture by dry regenerable potassium based sorbents. 7th International Conference on Multiphase Flow, ICMF 2010, US, May 30 – June 4, 2010. [9] Park SW, Sung DH, Choi BS, Lee JW, Kumazawa H. Carbonation kinetics of potassium carbonate by carbon dioxide. J Ind Eng Chem 2006; 4:522-530. [10] Kongkitisupchai S, Gidaspow D. Carbon dioxide capture using solid sorbents in a fluidized bed with reduced pressure regeneration in a downer. AIChE J 2013; 12:4519-4537.

 

 

Chattan Sakaunnapaporn et al. / Energy Procedia 138 (2017) 518–523 523 Author name / Energy Procedia 00 (2017) 000–000 5

(a) (b)

Fig. 3. (a) Contour of solid volume fraction and (b) contour of CO2 mass fraction (at three different quasi-steady state simulation times).

3.3 Analysis of variance for the statistical experimental design

The 2k factorial statistical experimental design methodology (with literature base case condition) is useful in performing the experiment due to its many advantages. It gives the smallest number of runs for k factors. However, the full parameter analysis can still be obtained. With this methodology, the two levels of each factor represent the low and high values. In this study, the statistical experimental design had the inlet gas velocity as a first factor and solid circulation rate as a second factor. The response variable was CO2 removal percentage at the outlet of circulating fluidized bed riser. The analysis of variance result for the statistical experimental design is summarized in Table 2. The p–value was used for the statistical testing. If the p–value is lower than 0.05, the factor significantly affects the interested response. From the results, it can be summarized that inlet gas velocity had significantly affected on the CO2 removal percentage. In addition, it was found that effect of the solid sorbent loading and the interaction between inlet gas velocity and solid sorbent loading did not have an effect on the CO2 conversion significantly. Fig. 4 illustrates the main effect plot of the inlet gas velocity and the solid circulation rate on the CO2 removal percentage. When increasing the inlet gas velocity and the solid circulation rate, the CO2 removal percentage was lower and higher, respectively. The high gas velocity will decrease the system residence time and reduce the contacting between gas and solid particles. The high solid circulation rate will increase the quantity of reactant material of the adsorption inside the circulating fluidized bed riser.

Fig. 5 shows the response surface of CO2 removal percentage with the changing of inlet gas velocity and the solid circulation rate. The response surface can be used to choose the operating condition with desired outcome or response. For this circulating fluidized bed riser, the highest CO2 removal percentage is preferred. Therefore, the low inlet gas velocity and high solid circulation rate is needed to operate the system to obtain the high CO2 removal percentage.

Table 2. The analysis of variance result for the statistical experimental design.

Source Sum of DF Mean F Prob > F Squares Square Value

A 3076.67 1 3076.67 171.75 0.05 B 440.82 1 440.82 24.61 0.13

AB 303.33 1 303.33 16.93 0.15 Residual 17.91 1 17.91 Cor Total 3920.26 4

 

6 Author name / Energy Procedia 00 (2017) 000–000

 

Fig. 4. This study main effect plot. Fig. 5. This study response surface contour.

4. Conclusion

In this study, the computational fluid dynamics model which had 10,000 mesh cells and three reaction kinetic models was accurately used to predict CO2 removal percentage and system hydrodynamics of circulating fluidized bed riser comparing with the experimental results of Yi et al. [3]. From the 2k factorial statistical experimental design (with literature base case condition), the increasing of inlet gas velocity and solid sorbent circulation rate gave lower and higher CO2 removal percentage, respectively. In addition, the analysis concluded the significant effect of inlet gas velocity on the CO2 removal. The low inlet gas velocity and high solid circulation rate is needed to operate the system to obtain the high CO2 removal percentage.

Acknowledgements

This study was financially supported by the Scholarship from the Graduate School, Chulalongkorn University to commemorate the 72nd anniversary of his Majesty King Bhumibol Aduladej, the 90th Anniversary of Chulalongkorn University Fund, the Graduate School Thesis Grant, the National Research Council of Thailand, the Thailand Research Fund for fiscal year 2016–2019 (RSA5980052), and Ratchadapisek Sompoch Endowment Fund (2016), Chulalongkorn University (CU-59-003-IC).

References

[1] Abanades JC, Antrony EJ, Wang, J, Oakey JE. Fluidized-bed combustion system integration CO2 capture with CaO. Environ Sci Technol 2005; 39:2861–2866. [2] Wang S, Wang Q, Chen J, Liu G, Lu H, Sun L. Assessment of CO2 capture using potassium-based sorbents in circulating fluidized bed reactor by multiscale modeling. Fuel 2016; 164:66–72. [3] Yi CK, Jo SJ, Seo Y, Lee JB, Ryu CK. Continuous operation of the potassium-based dry sorbent CO2 capture process with two fluidized-bed reactors. Int J Greenhouse Gas Control 2007; 1:31-36. [4] Zhao C, Chen X, Zhao C, Wu Y, Dong W. K2CO3/Al2O3 for capturing CO2 in flue gas from power plants. Part 3: CO2 capture behaviors of K2CO3/Al2O3 in a bubbling fluidized-bed reactor. Energy Fuels 2012; 26:3062–3068. [5] Yafei G, Chuanwen Z, Xiaoping C, Changhai L. CO2 capture and sorbent regeneration performances of some wood ash materials. Appl Energ 2015; 137:26–36. [6] Emadoddin A, Hamid A. CFD simulation of CO2 sorption in a circulating fluidized bed using deactivation kinetic model. 10th International Conference on Circulating Fluidized Beds and Fluidization Technology – CFB-10, US, May 1 – May 5, 2011. [7] Chalermsinsuwan B, Piumsomboon P, Gidaspow D. Kinetic theory based computation of PSRI riser: Part I–Estimate of mass transfer coefficient. Chem Eng Sci 2009; 64:1195–1211. [8] Garg R, Shahnam M, Huckaby ED. Continuum simulations of CO2 capture by dry regenerable potassium based sorbents. 7th International Conference on Multiphase Flow, ICMF 2010, US, May 30 – June 4, 2010. [9] Park SW, Sung DH, Choi BS, Lee JW, Kumazawa H. Carbonation kinetics of potassium carbonate by carbon dioxide. J Ind Eng Chem 2006; 4:522-530. [10] Kongkitisupchai S, Gidaspow D. Carbon dioxide capture using solid sorbents in a fluidized bed with reduced pressure regeneration in a downer. AIChE J 2013; 12:4519-4537.

Describe a chemical-related safety or environmental hazard

/in /by

Individual Case Study Homework 50 pts CHE 432 – Spring 2018

Choose one unique topic (different from your classmates) from one of the two categories below.

• Describe a chemical-related safety or environmental hazard that is related to your design project. Suggested content:

o Background of the process and plant o Chemical involved o What caused the disaster? o What impact did the disaster had on the local population, society, environment,

and chemical industry? o How a better design could have prevented such a catastrophe, etc.? o Example: If you reactor involves catalyst, you could summarize a CSB report on

an incident involving reactors using solid catalysts. Alternatively, rather than a specific incident, you may elect to describe a chronic chemical issue (e.g. acid rain, lead in gasoline, etc).

• OR Report on a current event related to chemical engineering and the social and political implications.

o Be as non-biased as possible. o Support the various views on the topic with information. Discredit non-logical

claims with information. o Example: Potential elimination of funding for the Chemical Safety Board in 2019.

(A House committee funded it in July of last year.)

If you have another topic which you think is interesting but does not meet these criteria exactly, please check with your instructor for approval.

• Write no more than 1 page of text. Use photos, figures and diagrams as appropriate (this will increase the page count if used).

• Scored on: o How does the topic relate to your design project or your area of interest? o Technical description and how clearly presented. o Clear guidance on how the topic could be prevented/improved in the future.

• Upload your file to Canvas by the due date.

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