Development of a coke oven gas assisted coal to ethylene glycol

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Development of a coke oven gas assisted coal to ethylene glycol process for high techno-economic performance and low emission Qingchun Yang, Chenwei Zhang, Dawei Zhang, and Huairong Zhou Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b00910 • Publication Date (Web): 17 May 2018 Downloaded from http://pubs.acs.org on May 18, 2018

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Industrial & Engineering Chemistry Research

1 2 3 4

Development of a coke oven gas assisted coal to

5

ethylene glycol process for high techno-economic

6

performance and low emission

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Qingchun Yanga*, Chenwei Zhanga, Dawei Zhanga, Huairong Zhoub

8 9 10

a School of Chemistry and Chemical Engineering, Hefei University of Technology,

11

Hefei, PR China, 230009

12

b School of Chemistry and Chemical Engineering, South University of Technology,

13

Guangzhou, 510641, PR China

14 15 16

+ For publication in Industrial & Engineering Chemistry Research

17 18

*Corresponding author:

19

Qingchun Yang Ph.D.

20

School of Chemistry and Chemical Engineering

21

Hefei University of Technology

22

Hefei, 230009, P. R. China.

23

Phone: +86-13167739808

24

Email: [email protected]

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ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

Abstract

2

Developing coal to ethylene glycol (CtEG) process is of great interest to many

3

countries, especially in China. However, because the hydrogen to carbon ratio of the

4

coal gasified gas is far less than the desired value, the CtEG process suffers from high

5

CO2 emission and wastes precious carbon resources. At the same, most of coke oven

6

gas (COG) is discharged directly or used as fuel, resulting in a waste of resources,

7

serious environmental pollution and economic loss. To efficient and clean utilization

8

of coal and COG resources, this paper proposed a novel coke oven gas assisted coal to

9

ethylene glycol (CaCtEG) process. The proposed process introduces the

10

hydrogen-rich COG to adjust the hydrogen to carbon ratio and reduce CO2 emission

11

by integrating a dry methane reforming unit. Key operational parameters are

12

investigated and optimized based on the established mathematic model. The

13

advantages of the process are studied by a detailed techno-economic analysis. Results

14

show that, compared with the conventional CtEG process, the CaCtEG process is

15

promising since it increases the carbon element and exergy efficiency by 18.35% and

16

10.59%. The CO2 emission ratio of the proposed process is reduced from 2.58 t/t-EG

17

to 0.44 t/t-EG. From the economic point of view, the CaCtEG process can save

18

production cost by 5.11% and increase the internal rate of return by 3.41%. The

19

capital investment, however, is slightly increased because of the two additional units.

20 21

Keywords: coal to ethylene glycol; coke oven gas; techno-economic analysis; CO2

22

mitigation; dry methane reforming

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2


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1. Introduction

2

Ethylene glycol (EG), one of the most important platform chemicals, is used in

3

production of large numbers of derivative chemicals.1 However, EG production

4

currently meets the severe dilemma which the rapid development of polyester

5

industry worsens the conflict between the supply and demand of EG. This problem is

6

even worse in China where the dependence on foreign EG is higher than 60%. The

7

traditional EG production technologies (oil-based routes), represented by the ethylene

8

oxide hydration technology, cannot greatly increase the EG production capacity

9

because that its growth rate of EG production capacity is subject to the supporting

10

ethylene plant. Besides, this technology is criticized by the significant drawbacks of

11

high production cost, high energy and water consumption.2 Therefore, many countries,

12

especially in China, endeavor to explore other resources for EG production.3 For

13

example, China is making a great effort to develop alternatives to oil-based routes.

14

The key technical breakthrough is the successful commercialization of more than ten

15

large-scale coal to ethylene glycol (CtEG) plants, which is widely distributed in

16

Xinjiang, Henan, and Inner Mongolia, China.4 In addition, there are more than thirty

17

coal to ethylene glycol plants under construction or preparatory work in China. Thus,

18

the coal to ethylene glycol process is developed to be one of the independent and

19

mainstream coal chemical processes.

20

The flowsheet of a conventional CtEG process is shown in Figure 1. It is

21

considered as the benchmark in this paper. Coal is fed into the coal gasification (CG)

22

unit to be gasified to crude syngas after pretreatment. To adjust the

23

hydrogen-to-carbon ratio (H/C), part of the syngas is sent to the water gas shift (WGS)

24

unit, in which a lot of precious carbon resources are wasted to CO2. Then the syngas

25

enters the gas separation and purification (GSP) unit to remove acid gases as well as

26

produce high-purity H2 and CO. The CO stream is then fed into the dimethyl oxalate

27

synthesis (DMOS) unit to obtain dimethyl oxalate (DMO). The H2 stream is reacted

28

with DMO to produce crude EG in the ethylene glycol synthesis (EGS) unit. Finally, 3



1

the crude EG is sent to the ethylene glycol refining (EGR) unit to produce high-purity

2

EG products (99.8 wt%).

3

However, the CtEG process suffers from the problems of higher CO2 emission,

4

lower carbon utilization, and energy efficiency compared with the oil-based routes.5

5

Man et al. conducted an environmental impact and techno-economic analysis of the

6

coal gasification process.6 They found that the coal gasification is accompanied by a

7

large number of CO2 emissions. Furthermore, the required H/C ratio for EG

8

production is about 2, however, that of the crude syngas is less than 1.0 in generally,

9

which is far less than the desired value for the CtEG process.6 Thus, syngas is

10

converted into H2 by the WGS reaction, resulting in a high emission and waste of

11

carbon resources.7 As a result, the CO2 emission of the CtEG process is about 3.1

12

t/t-EG.8 The high CO2 emission leads to serious loss of carbon element. If introducing

13

a carbon tax equal to or higher than $60/t- CO2, the cost advantages of the CtEG

14

process could no longer be present.5 In a word, the CtEG process has be fruitfully

15

developed in China because of the abundant reserve of coal and the low production

16

cost. However, development of the CtEG industry is criticized by the high emissions.

17

Therefore, it is urgent to reduce the CO2 emission and improve the techno-economic

18

performance of the CtEG process.

19

Integration of H2-rich resources to the coal based chemical engineering process

20

is considered as an effective method to address these issues.9-11 Coke oven gas (COG),

21

one of H2-rich resources, mainly consists of H2 (55-60%), CH4 (23-27%), CO (5-8%),

22

and N2 (3-5%) as well as some impurities, such as CO2, H2S, NH3 and COS.12 In

23

China, the annual production of COG is about 7×1010 m3.10 Unfortunately, most of

24

them is directly discharged into the atmosphere.11 It results in serious environmental

25

pollutant and a waste of valuable resources. It is a meaningful work to comprehensive

26

use COG resources. Considering that syngas has high carbon contents; while COG

27

has high hydrogen contents, it not only can take advantages of coal and COG to

28

obtain syngas with a suitable H/C ratio, but also improve system techno-economic

4


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1 2

performance.13,14 Man et al. developed a co-feed process of coke oven gas assisted coal to

3

olefins.15 Results show that the CO2 emission of the novel process is decreased by 85%

4

and energy efficiency increased by 10% compared with the conventional one.

5

Moreover, they also proposed a co-feed process of coal and COG to synthetic natural

6

gas, which the CO2 emission is reduced by 60% and the energy efficiency is increased

7

by 4% in comparison to the conventional process.16 Yi et al. proposed a process of

8

CO2 recycle assistance with coke oven gas to synthetic natural gas where the energy

9

and exergy efficiency is increased by 6.3 % and 6.6%, as well as the production cost

10

and direct CO2 emission reduced by 0.05 $/m3 and 99.9%.11 Gong et al. designed a

11

process of CO2 recycle to supply carbon for assisting with coke oven gas to methanol

12

process.17 As a result, it realizes clean and efficient COG utilization. There are also

13

several commercial plants introduces this technology to enhance their element and

14

energy efficiencies.17 To date, however, few studies have been reported on integrated

15

COG to the CtEG process for lower CO2 emission and high techno-economic

16

analysis.

17

According to the above discussion, a coke oven gas assisted coal to ethylene

18

glycol (CaCtEG) process is proposed to efficient utilization of coal and COG

19

resources for reducing CO2 emission and enhancing its techno-economic performance.

20

In the proposed process, COG is introduced to assist the CtEG process to reduce the

21

shift ratio of syngas and save carbon element. The dry methane reforming technology

22

is integrated to the CaCtEG process to reuse CO2 and increase carbon efficiency.

23

The main contributions of the paper are: (a) to conceptual design, model and

24

simulate the novel CaCtEG process after comprehensively considering the

25

characteristics of conventional CtEG process; (b) to investigate and optimize the

26

effect of key operational parameters on the performance of the CaCtEG process; (c) to

27

manifest the promising strengths of the proposed process in terms of carbon element

28

efficiency, CO2 emission ratio, exergy efficiency, capital investment, production cost,

5



1

and internal rate of return.

2

2. Novel coke oven gas assisted coal to ethylene glycol

3

process

4

The novel coke oven gas assisted coal to ethylene glycol (CaCtEG) process is

5

proposed on the basis of the conventional CtEG process as shown in Figure 2. The

6

CaCtEG process mainly consists of nine units: the coal gasification (CG)unit, water

7

gas shift (WGS) unit, gas separation and purification (GSP) unit, EG synthesis (EGS)

8

unit, EG refining (EGR) unit, dimethyl oxalate synthesis (DMOS) unit, air separation

9

unit (ASU), COG separation (COGS) unit, and dry methane reforming (DMR) unit.

10

Different from the conventional CtEG process, COG is introduced to assist CtEG

11

process to decrease the shift ratio of the crude syngas; and dry methane reforming

12

(DMR) technology is integrated to recycle use CO2 produced by the process as well as

13

efficient use the CH4 in COG. COG is firstly sent to the COGS unit to desulfurization

14

and separation. Because H2 is the richest component in COG, so the novel process is

15

easier to get a suitable H/C ratio for EG production. The CH4 stream out from the

16

COGS unit is fed to the DMR unit where CH4 is reacted with CO2 and converted to

17

produce CO and H2 (CH4 + CO2 → 2CO + 2H2). Because DMR technology is an

18

effective method to reuse CO2 from coal gasification process, this technology is

19

considered as one of promising CO2 mitigation techniques.18,19 It is widely used in

20

COG to different fields, such as methanol, olefins, synthetic natural gas, and dimethyl

21

ether. 20-22

22

Since the DMR unit can utilize the CH4 separated from COG and CO2 produced

23

from coal gasification process to generate more syngas, the carbon utilization

24

efficiency and the EG production are greatly increased.

25

3. Steady-state simulation of the CaCtEG process

26

Modeling and simulation of the CaCtEG process is performed prior to the

6


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1

detailed feasibility analysis. Although the CaCtEG process is complex and involves

2

nine different units, to limit the length of this paper, this article is focused on the

3

description of the modeling of three key units. They are the CG unit, the EGS unit,

4

and the DMR unit. The detailed modeling and simulation of the rest units can be

5

found in the works.16,23 A simplified modeling flowsheet of the CaCtEG process is

6

present in Figure 3, and the key operational conditions required for the simulation are

7

listed in Table S1 in Supporting Information.

8

3.1 Modeling of the CG unit

9

After pretreatment, the dry coal is fed into the gasifier along with the oxygen

10

produced by the ASU unit. Holingola coal is selected as the raw material. Its

11

proximate and elementary analysis results are listed in Table 1. The processing

12

capacity is referred to a practical CtEG plant located in Holingola city, China, which

13

is about 9.52 ×105 t/y. The coal is converted to crude syngas which mainly consists of

14

CO, H2 and CO2. During the modeling and simulation, coal is treated as

15

unconventional solid in this work. RK-SOAVE method is selected as the physical

16

property of the CG unit. The coal drying reactions are modeled by a RStoic model,

17

and its pressure and temperature are set to 4 MPa and 300°C. The output of the drying

18

reactor is sent to a gas-solid separator (Sep model) to remove water. The dried coal

19

enters the pyrolysis reactor in which is to pyrolyze the coal to produce CO, H2, CO2,

20

CH4, H2O, H2S, N2, char and tar. A Ryield model is used to model and simulate the

21

pyrolysis reaction as formulated in Eq. (1).

22

Coal → CO + H2 + CO2 + CH4 + H2O + H2S + N2 + Char + tar

23

The pyrolysis products are fed into a separator model to separate the char and gas.

24

The char is then sent to the gasification reactor which is modeled by a Gibbs free

25

energy minimization reactor (RGibbs model). The reaction equation is written as Eqs.

26

(2) to (7).24

27

C+

Z +2 Z 1 O2 → CO + CO 2 2Z + 2 Z +1 Z +1 7


(1)

(2)


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1

C＋ CO2 → 2CO

(3)

2

C ＋ H2O → CO + H2

(4)

3

C ＋2H2 →CH4

(5)

4

2H2＋ O2 →2H2O

(6)

5

CO + H2O → CO2 + H2

(7)

6

where the parameter Z depends on the reaction temperature (T) and is calculated by

7

Eq (8).24

8

Z=

9

The crude syngas is obtained after the gasified gas mixed with the gas streams

10

out from the drying and pyrolysis reactors. The three-level heat exchanger was used

11

and modeled by three HeatX models for recovering waste heat of the output syngas

12

heat.25

13

3.2 Modeling of the DMR unit

6249 − [CO ] = 2500e T [CO2 ]

(8)

14

To reduce CO2 emissions, the DMR unit is integrated to the CtEG process. CH4

15

from the COGS unit is mixed with the CO2 recycled from the GSP unit and then

16

preheated by the output of the DMR reactor. The preheated mixture is sent to the

17

DMR reactor where CH4 reacted with CO2 to produce CO and H2 as shown in Eq. (9).

18

However, it is simultaneously to occur a side reaction as shown in Eq (10). The

19

Peng-Robinson method is used for modeling.26 A RPlug model is selected to model

20

DMR reactions. Ni-based catalyst is used for the DMR reaction because of its

21

excellent catalytic activity and low cost.27

22

CH4 + CO2 ⇋ 2CO + 2H2; ∆ H = +247 kJ/mol

(9)

23

CO2 + H2 ⇋ CO + H2O; ∆ H = + 41.2 kJ/mol

(10)

24

Langmuir-Hinshelwood reaction rate equation is used for calculation of the

25

dynamics of the DMR reaction as shown in Eq. (11)

8


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1

rDMR =

(

(

2 k WGS K CH4 K CO2 pCH4 pCO2 − pCO pH2 2 / K eq −0.25 H2

1+ p

pCH4 K CH4 + K CO2 pCO2 p

))

0.25 H2

(11)

2

where rDMR and Keq denote the reaction rate and reaction equilibrium constant of the

3

DMR reaction; KCO2 and KCH4 are the absorption equilibrium constants of CO2 and

4

CH4; pCO, pH2, pCH4, and pCO2 mean the partial pressures of CO, H2, CH4, and CO2,

5

respectively. These kinetic parameters can be found in the works.26,27

6

3.3 Modeling of the EGS unit

7

After mixed with the hydrogen streams, the DMO enters the hydrogenation

8

reactor (RPlug model). In this reactor, the DMO is firstly reacted with hydrogen to

9

produce methyl glycolate (MG). Then, MG is further converted to EG which is

10

accompanied by side reaction to produce ethanol (ET) as formulated in Eqs. (12)

11

-(14).23

12

DMO + 2 H2 → 2 MG + CH3OH

(12)

13

MG + 2 H2 → 2 EG + CH3OH

(13)

14

EG + H2 → ET+ CH3OH

(14)

15

A RPlug model is adopted to model EG synthesis reactor. The kinetic of the

16

above three reactions are shown as follows:3,28 k1 K DMO ( PDMO PH −

17

rMG =

(1 + K DMO PDMO +K MeOH PMeOH + K MG PMG + K EG PEG + K ET PET ) k 2 K MG ( PMG PH −

18

rEG =

19

rET =

PMG PMeOH ) K p1 PH

PEG PMeOH ) K p2 PH

(1 + K DMO PDMO +K MeOH PMeOH + K MG PMG + K EG PEG + K ET PET )

k3 K EG PEG PH (1 + K DMO PDMO +K MeOH PMeOH + K MG PMG + K EG PEG + K ET PET )

(15)

(16)

(17)

20

where ri is the reaction rate of ith equation; Pj denotes the partial pressure of j

21

compound. The equilibrium constant (K) and reaction rate constant (k) of these

22

equations are present in Table 2. 9



1

The output of the DMO hydrogenation reactor firstly enters the heat exchanger

2

(HeatX model) to recovery the waste heat and preheat the feedstock of the reactor. It

3

is then fed into the high-pressure separator to obtain crude EG product. Most of the

4

gas stream from the separator is recycled to the compressor, and the rest is discharged

5

as tail gas. After reduced pressure, the crude EG is got into the EGR unit for

6

production of high-purity EG product.

7

3.4 Analysis of key operational parameters

8

According to the previous discussions, the H/C ratio is important for EG

9

synthesis reaction. Therefore, the effect of the feedstock ratio of COG to coal

10

(COG/Coal) and the shift ratio of syngas (αCO) on the H/C ratio and elementary

11

efficiency of carbon (EC) is analyzed and optimized firstly. To more effectively utilize

12

COG resources, the key operational parameters, such as feedstock ratio of CH4 to CO2

13

and pressure, are discussed in this paper.

14

3.4.1 Effect of the COG/Coal and αCO on H/C ratio and resource utilization

15

The optimal H/C ratio of EG synthesis is about 2.0. To obtain a suitable H/C

16

ratio, it can be easier achieved by changing the feedstock ratio of COG to coal

17

(COG/Coal) or the shift ratio of syngas (αCO) in the novel CaCtEG process. The effect

18

of the COG/Coal ratio and αCO on the H/C ratio is indicated in Figure 4. When both

19

COG/Coal ratio and αCO are equal to zero, results show that the H/C ratio of the

20

process is about 0.46, which is equal to the syngas produced from the CG unit. Due to

21

the H/C ratio of the syngas produced from the DMR process is less than 1.0, so the

22

H/C ratio of the CaCtEG process is far less than 2.0 if the process is without WGS

23

unit. Namely to efficient use the syngas, a WGS unit is still required for the CaCtEG

24

process. On the other hand, if the process does not integrate COG resource, the H/C

25

ratio is increased along with increasing αCO. Although it can obtain a suitable H/C

26

ratio, it will waste a lots of carbon element and emit a large of CO2. From the Figure 4,

27

either increasing the COG/Coal ratio or αCO can gradually increase the H/C ratio. 10


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1

However, the H/C ratio of the CaCtEG process is higher than 2.0 if the system has a

2

higher COG/Coal ratio and αCO. For example, when the COG/Coal ratio and αCO are

3

equal to 0.5 and 0.5, the H/C ratio is even higher than 3.0. As a result, it will reduce

4

the resource utilization efficiency of the CaCtEG process. Therefore, it is needs to

5

find an optimal feedstock ratio of COG to coal.

6

The elementary efficiency of carbon (EC), one of commonly used indexes for

7

analysis of resource utilization of chemical processes, is introduced in this paper. EC

8

is defined as:

9

EC =

out 2 FEG ×100% in in Fcoal + FCOG

in

(18)

in

10

where Fcoal and FCOG are the mole flow rate of carbon element in the input coal and

11

out COG; and FEG is the mole flow rate of the EG product.

12

The effect of the COG/Coal ratio and αCO on resource utilization is shown in

13

Figure 5. It can be concluded according to the Figure 5 that: (1) If only changing the

14

COG/Coal ratio, it is seen that the EC of the CaCtEG process is increased when the

15

COG/Coal ratio changes from 0 to be about 0.4. It mainly because that increasing the

16

mole flowrate of COG can reduce the split ratio of CO used for water gas shift

17

reaction. However, the EC of the CaCtEG process is decreased as the COG/Coal is

18

higher than 0.4 because excessive COG leads to a resource waste. (2) Similar as the

19

effect of αCO, the EC of the CaCtEG process is firstly increased and then decreased. It

20

is because if αCO is too small, the CO component is excessive; while if αCO is too large,

21

lots of CO component is converted to CO2. It needs to trade-off the EC and αCO.

22

Compared with the results of the effect of COG/Coal ratio, it can be seen that the

23

COG/Coal ratio has a greater impact on the EC. (3) The surface of the Figure 5 is

24

convex and has only one peak. It also means that there is a set of COG/Coal ratio and

25

αCO when the EC approaches the global optimal. (4) After optimization, the optimal

26

EC of the CaCtEG process is obtained when the COG/Coal ratio and αCO are equal to

27

0.4 t/t and 0.29. 11



1

3.4.2 Effect of CH4/CO2 ratio on the performance of the DMR unit

2

The CH4/CO2 ratio, one of the key parameters of the DMR unit, affects the

3

carbon utilization and the technical performance of the DMR unit. Therefore, the

4

effect of the CH4/CO2 ratio on the performance of the DMR unit is investigated and

5

indicated in Figure 6 (a)-(d). The reaction pressure is set to be 0.1 MPa.

6

Because the DMR reaction is a highly endothermic reaction, so the conversion of

7

CH4 is increased along with the temperature increased from 600°C to 1200°C as

8

shown in Figure 6(a). It is also seen that the conversion of CH4 is increased when the

9

CH4/CO2 ratio is decreased. But the differences of the CH4 conversion is slightly

10

changed with the different CH4/CO2 ratio when the temperature higher than 900°C.

11

Similar to the CH4 conversion, increasing the temperature or decreasing CH4/CO2

12

ratio has a positive effect on the CO selectivity as shown in Figure 6(b). It mainly

13

because a higher temperature promotes the DMR reaction, resulting in more carbon

14

element is converted into the CO component. As shown in Figure 6(c), it seen that

15

two different results of the H2 selectivity for CH4/CO2 ratio less than 1 and higher

16

than 1. As for the CH4/CO2 ratio is less than 1, the H2 selectivity is quickly increased

17

when the temperature is increased from 600°C to 900°C, and then gradually decreased

18

when the temperature is further increased. However, when the CH4/CO2 ratio is

19

greater than 1, the H2 selectivity is continually increased along with the increasing

20

temperature. These changing tends also show a good agreement with the results of

21

reported literature.29 Figure 6(d) indicates the effect of the CH4/CO2 ratio on the H/C

22

ratio. Results show that increasing the CH4/CO2 ratio can obtain a greater H/C ratio.

23

Besides, when the temperature increases from 600 to 900°C, the H/C ratio decreases

24

quickly; however, it is almost not changed when the temperature is above 900°C.

25

Although the H/C ratio at a lower temperature and a higher CH4/CO2 ratio can be

26

greater than two, the CH4 conversion as well as the selectivity of the H2 and CO are

27

relative low, resulting in waste of CH4 and low yield of products. Thus, a reasonable

28

value of the CH4/CO2 ratio and temperature is suggested to be 1:1 and 900°C in this 12


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1

paper.

2

3.4.3 Effect of pressure on the performance of the DMR unit

3

Since the DMR reaction is a reversible and volume increase reaction, the

4

pressure has a great impact on its reaction performance. In this paper, the effect of

5

pressure on the CH4 conversion, CO selectivity, H2 selectivity, and H/C ratio is

6

analyzed and shown in Figure 7 (a)-(d).

7

Because of the characteristics of endothermic reaction, the CH4 conversion

8

increases at different pressure when the temperature is increased as illustrated in

9

Figure 7(a). It is also seen that the CH4 conversion is decreased along with the

10

increases in pressure. This is due to the DMR reaction is a volume increase reaction.

11

The high pressure can inhibit this reaction. As shown in Figure 7(b), it is clear that

12

high pressure has a negative effect on the CO selectivity. It is because of the limitation

13

from the Le Chatelier’s Principle. But reacted under the high pressure, the

14

temperature has a less impact on the CO selectivity since the trend of change is more

15

and more smooth. As to the H2 selectivity, the trends are similar to the CO selectivity,

16

which the temperature has a positive impact on the H2 selectivity, but the pressure is

17

negative as shown in Figure 7(c). The H/C ratio is increased when the pressure is

18

increased from 0.05 MPa to 5 MPa as shown in Figure 7(d). But if the temperature is

19

higher than 900°C, the H/C ratio is slightly changed. Because if pressure is too small,

20

it could greatly increase the reaction volume and even need more additional cost for

21

maintaining negative pressure, while the CH4 conversion and the selectivity of the CO

22

and H2 is relatively high at 0.1 MPa (atmospheric pressure), so the pressure of the

23

DMR reaction is suggested to 0.1 MPa in this paper.

24

3.5 Simulation results and discussion

25

As discussed in the above section, the ratio of COG/Coal and the shift ratio of

26

syngas (αCO) are set to be 0.4 and 0.29 for maximum carbon utilization in the course

27

of novel process design. For make full use of the COG resource, the CH4/CO ratio, 13



1

temperature, and pressure of the DMR reactor are selected to 1:1, 900°C, and 0.1 MPa,

2

respectively. In terms of the Aspen Plus software, the whole CaCtEG process is

3

modeled and simulated. The simulation results of the main streams marked in Figure

4

3 are present in Table S2 in Supporting Information. The mass balance of the CaCtEG

5

process is shown in Figure 8; while the key information of the mass balance of the

6

conventional CtEG process can be found in Figure S1 in the Supporting Information.

7

It is seen that 47.59 t/h COG is used as hydrogen-rich resource to reduce CO2

8

emission. 116.45 t/h CO with the purity of 99.06% are obtained after the GSP unit.

9

9.88 t/h H2 from the GSP unit mixed with the 5.66 t/h H2 produced from the COGS

10

unit are reacted with 202.96 t/h DMO in the EGS unit, where 112.17 t/h crude EG is

11

obtained. After the EGR unit, 103.05 t/h EG product is finally produced with the

12

purity higher than 99%.

13

For validation of the accuracy of the model, this paper compares the simulation

14

results of key composition of the gas streams, as well as the purity of intermediate and

15

target products results with the industrial data as shown in Figures S2 and S3 in the

16

Supporting Information. It can be seen that the results are in good agreement with the

17

industrial data. Thus, the established model can be used for the subsequent system

18

analysis.

19

4. Comparison between the CtEG and CaCtEG

20

processes

21

To manifest the advantages of the CaCtEG process, a detailed techno-economic

22

analysis is performed and compared with a conventional CtEG process, which is one

23

of practical CtEG plants located in Holingola city, China. The elementary efficiency

24

of carbon (EC), CO2 emission ratio, and exergy efficiency are introduced as the

25

technical indexes; while the total capital investment, production cost, and internal rate

26

of return are used to compare the economic performance of these two processes.

14


Page 14 of 46

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1 2

4.1 Technical performance In this paper, the carbon utilization and exergy efficiency is used for comparison

3

of the technical performance of the two processes.

4

4.1.1 Efficiency of Carbon utilization

5

To identify the efficiency of carbon utilization of the CtEG and the CaCtEG

6

processes, the equivalent carbon element balance of the two process is investigated

7

firstly and indicated in Figure 9. According to the elementary analysis of the raw coal,

8

there are about 5737 kmol·C/h fed into the CG unit and 3700 kmol·C/h are introduced

9

into the syngas. From the equivalent carbon element balance results of the WGS unit,

10

it is seen that 71.0% carbon element are not shifted in the WGS unit, which is greatly

11

higher than that of the CtEG process, 50.8%. It means that 20.2% more carbon

12

element will be contained in CO rather than CO2. As to the GSP unit, about 54.8%

13

carbon element are recycled to the DMR unit and reacted with 1680 kmol·C/h carbon

14

(including CH4, CO and CO2) from the COG to produce 2928 kmol·C/h carbon. Due

15

to the side reactions and waste, the loss of equivalent carbon element of the EGS and

16

DMOS unit is about 206 and 811 kmol·C/h, respectively. After a series of separation

17

and purification processes, there are 3324 and 1210 kmol·C/h contained in the EG

18

product of the CtEG and the CaCtEG processes.

19

According to the equivalent carbon element balance, the carbon utilization

20

efficiency of the CtEG and the CaCtEG processes are determined and shown in the

21

Figure 10. The carbon element efficiency of the CaCtEG process is increased from

22

21.23% to 39.58%. The CO2 emission ratio of the CaCtEG process, which is defined

23

as the ratio of the mass flowrate of CO2 to that of EG product, is significantly reduced

24

from 2.58 t/t-EG to 0.44 t/t-EG. It mainly because less syngas takes place in water

25

shift gas reaction. COG, one of hydrogen-rich resources, will waste less carbon

26

element to get the same amount of EG. It therefore can say that the CaCtEG process is

27

more efficient than the CtEG process from carbon utilization efficiency. 15



1

Page 16 of 46

4.1.2 Exergy efficiency

2

The inefficiency of the coal-based chemical process can be quantitatively

3

identified by exergy analysis.30 The exergy of a stream (Ex) and the exergy balance of

4

the whole system can be written as follows.31,32

5

Ex =Exph + Exch + ∆ mix Ex

(19)

6

Exin,tot = Exproduct,tot + Exdestruction,tot + Exothers,tot

(20)

7

Exergy efficiency (ψ), one of important indicators to address this issue, can be

8

defined as the ratio of exergy of the target product and the input as expressed in Eq.

9

(21).33

10

ψ=

Exproduct, tot Exin, tot

× 100% =

ExEG × 100% Excoal + ExCOG + Exutilities

(21)

11

where Excoal, ExCOG, and Exutilities are the input exergy of coal, COG, and utilities; ExEG

12

denotes the target exergy of EG product.

13

Based on the exergy balance of the CtEG and the CaCtEG processes (shown in

14

Table S3 in the Supporting information), the exergy efficiency of these two processes

15

is shown in Figure 11. Compared to the CtEG process, the exergy efficiency of the

16

CaCtEG process is increased from 30.68% to 41.27%. This is because that the DMR

17

unit is a more efficient unit to produce syngas from both exergy efficiency and

18

resource efficiency. Besides, the same mass flowrate of carbon in the CaCtEG process

19

can produce more EG products, resulting in the exergy destruction and exergy loss of

20

the CaCtEG process are greatly decreased in comparison of those of the CtEG process.

21

Thus, thanks to the introduction of COG, the CaCtEG process has a better technical

22

performance than the CtEG process.

23

4.2 Economic performance

24

For introducing a new process to be industrialized, it is needed to analyze its

25

economic performance. In this paper, because of the wide application of the total

16


Page 17 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

capital cost (TCI), the total production cost (TPC), and internal rate of return (IRR),33

2

they are introduced to manifest the economic advantages of the proposed process.

3

4.2.1 Analysis of TCI

4

The TCI is the sum of the fixed capital and the working capital investments,34

5

and can be easily calculated by the ratio factor (RF) multiplied by the total purchased

6

equipment cost (TPEC).35-37 It can be written as the Eq. (20).38 As to the CtEG

7

industry, the RF needs to be modified referring to the local situation of the plant. In

8

this paper, the assumptions of RF are listed in the Table S4 in the Supporting

9

Information.

10

TCI = (1 + RF ) × TPEC

11

The equipment cost, one of the most important components in TPEC, can be

12 13

(22)

estimated by the scaling factor method as expressed in Eq. (23).39  Q  I =Iθ × θ ×    Qθ 

sf

(23)

14

where I and Q are the equipment cost and processing capacity of the proposed process;

15

Iθ and Qθ mean these of the reference plant; θ denotes the domestic factor; sf is the

16

production scale factor. The equipment cost for different units of the CtEG and

17

CaCtEG processes are calculated on the basis of the investment benchmark of these

18

units as listed in Table 3.

19

According to the Eqs. (22) and (23), the TCI of the two processes is calculated

20

and indicated in Figure 12. It can be seen that the TCI of the CaCtEG process

21

increases from 1.66×104 CNY/t-EG to 1.76×104 CNY/t-EG. It is mainly because that

22

the CaCtEG process introduces two additional units, the COGS and DMR units. It

23

obviously increases the equipment cost as well as others costs of the CtEG process.

24

4.2.2 Analysis of TPC

25

TPC, another significant economic indicator, consists of six parts: the raw material

26

cost (CR), the utilities cost (CU), the operating and maintenance cost (COM), the fixed 17



Page 18 of 46

1

charge (CFC), the plant overhead cost (CPOC), and the general expenses (including the

2

distribution, the selling cost and the administrative cost, CGE), as shown in Eq. (24).40

3

The basic data for calculation of the CR and CU are listed in Table 4; while the rest

4

costs are estimated according to the previous works of Yang et al.41 and Parkinson et

5

al.42, as shown in Table S5 in the Supporting Information.

6

TPC = CR + CU + COM + CFC + CPOC + CGE

7

The TPC and its distribution are finally obtained by the Eq. (24) as present in

8

Figure 13. The raw material cost of the CaCtEG process is significantly decreased by

9

24.1% due to the low-price and efficient utilization of COG. It is also an advantage of

10

CaCtEG process to integrate CO2 and COG. However, because the CaCtEG process is

11

more complexity than the CtEG process, so the other cost of the CaCtEG process is

12

slightly increased. As a result, the TPC of the CtEG and CaCtEG processes are 4910

13

and 4659 CNY/t-EG/y. Therefore, integrating the COG resource to the CtEG process

14

can greatly reduce its production cost and improve its economic performance.

15

4.2.3 Analysis of IRR

(24)

16

Because IRR can effectively reflect the dynamic economic benefit of one

17

project,17 so it is used for further manifest the advantages of the proposed process in

18

this paper. It can be defined as the discount rate that equates the present value of the

19

project’s future net cash flows with the project’s initial cash outlay, as shown in Eq.

20

(25).43 N

21

∑ C × (1 + IRR ) t

t

=0

(25)

t =0

22

where Ct means the net cash flow of year t.

23

Considering that the tax rate is equal to 25%, the IRR of the CtEG and CaCtEG

24

processes are 15.12% and 18.53% as shown in Figure 14. This is because that the

25

production cost of the proposed process is greatly saved and it can produce more EG

26

product in the proposed process with wasting less carbon element. Therefore, the

27

CaCtEG process has a better economic performance than the CtEG process. However, 18


Page 19 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

for industrial implementation, it would increase the capital investment and production

2

cost of the conventional CtEG process since the novel process integrated with a dry

3

methane reforming unit. In addition, we should pay more attention to its heat

4

exchanger network and water network because because the degree of integration of

5

the CaCtEG process is increased.

6

5. Conclusions

7

In the momentum of reducing CO2 emission of the coal to ethylene glycol (CtEG)

8

process, a novel coke oven gas assisted coal to ethylene glycol (CaCtEG) process is

9

proposed in this paper. The hydrogen-rich source, COG, is introduced for CO2

10

mitigation by integrating a dry methane reforming unit. For analysis of the proposed

11

process, the mathematic model of the whole CaCtEG flowsheet is established and

12

simulate along with the investigation of the key parameters. Then the advantages and

13

disadvantages of the proposed process are analyzed and compared to the conventional

14

process. The main conclusions are drawn briefly as follows:

15

(1) The CaCtEG process takes the advantages of the wasted COG in China’s coke

16

industry. It is helpful to improve the economic benefit of COG and protect

17

environment.

18

(2) The key parameters are analyzed and optimized on the basis of the established

19

model. The COG/Coal ratio and shift ratio of syngas (αCO) are suggested to be

20

0.4 and 0.29 for optimizing the resource utilization of the CaCtEG process.

21

For efficient utilization of COG, the CH4/CO2 ratio, temperature, and pressure

22

of the DMR reaction is suggested to 1:1, 900°C, and 0.1 MPa.

23

(3) The CaCtEG process has a better technical performance than the conventional

24

process. The carbon element efficiency of the CaCtEG process is increased

25

from 21.23% to 39.58%. The CO2 emission ratio is significantly reduced from

26

2.58 t/t-EG to 0.44 t/t-EG. As for its thermodynamic performance, the exergy

27

efficiency of the CaCtEG process is increased from 30.68% to 41.27%.

19



1

(4) Besides, the CaCtEG process has a better economic performance than the

2

conventional process. The production cost of the CaCtEG process is reduced

3

from 4910 to 4659 CNY/t-EG/y. The internal rate of return of the CaCtEG

4

process is increased from 15.12% to 18.53%.

5

(5) The proposed process will be more promising and competitive since it has a

6

better techno-economic analysis. However, the capital investment of the

7

proposed process is slightly increased.

8 9

Supporting Information The Supporting Information is available free of charge via the Internet at

10

http://pubs.acs.org/.

11

Acknowledgements

12

The authors are grateful for financial support from the National Natural Science

13

Foundation of China (No. 51472070) and the Hefei University of Technology projects

14

(No. 407-0371000045).

15

Nomenclature

16

CFC = fixed charge

17

CG = coal gasification

18

CGE = general expenses

19

COM= operating and maintenance cost

20

CPOC = plant overhead cost

21

CR = raw material cost

22

Ct = net cash flow of year t

23

CU = utilities cost

24

Ex = exergy

25

F = mole flow rate

26

I = equipment cost 20


Page 20 of 46

Page 21 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

K = absorption equilibrium constant

2

Keq = reaction equilibrium constant

3

k = reaction rate constant

4

Q = processing capacity.

5

Abbreviations

6

ASU = air separation unit

7

CaCtEG = coke oven gas assisted coal to ethylene glycol

8

COG = coke oven gas

9

COGS = coke oven gas separation

10

CtEG = coal to ethylene glycol

11

DMO = dimethyl oxalate

12

DMOS = dimethyl oxalate synthesis

13

DMR = dry methane reforming

14

EC = elementary efficiency of carbon

15

EG = ethylene glycol

16

EGR = ethylene glycol refining

17

EGS = ethylene glycol synthesis

18

ET = ethanol

19

GSP = gas separation and purification

20

IRR = internal rate of return

21

MG = methyl glycolate

22

sf = production scale factor

23

TCI = total capital cost

24

TPC = total production cost

25

TPEC = total purchased equipment cost

26

WGS = water gas shift

27

Greek letters

28

αCO = shift ratio of syngas

21



1

ψ = exergy efficiency

2

θ = domestic factor

3

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6156-6164.

25



1

[42] Parkinson, B.; Greig, C.; McFarland, E.; Smart, S. Techno-economic analysis of a process for

2

CO2-free coproduction of iron and hydrocarbon chemical products. Chem. Eng. J. 2017, 313,

3

136-143.

4

[43] Yang, M.; You, F. Comparative techno-economic and environmental analysis of ethylene and

5

propylene manufacturing from wet shale gas and naphtha. Ind. Eng. Chem. Res. 2017, 56 (14),

6

4038-4051.

26


Page 26 of 46

Page 27 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

Figures and Tables

2

Figures

3

Figure 1. Schematic diagram of the conventional CtEG process

4

Figure 2. Schematic diagram the novel CaCtEG process

5

Figure 3. Simplified flowsheet of the CaCtEG process

6

Figure 4. H/C ratio as different COG/Coal and αCO

7

Figure 5. Elementary efficiency of carbon as different COG/Coal and αCO

8

Figure 6. Effect of CH4/CO2 ratio on the performance of the DMR unit

9

Figure 7. Effect of pressure on the performance of the DMR unit

10

Figure 8. Mass balance of the whole CaCtEG process

11

Figure 9. Equivalent carbon balance of the CtEG and the CaCtEG processes

12

Figure 10. Carbon utilization efficiency of the CtEG and the CaCtEG processes

13

Figure 11. Exergy analysis of the CtEG and the CaCtEG processes

14

Figure 12. Distribution of the TCI of the CtEG and the CaCtEG processes

15

Figure 13. Distribution of the TPC of the CtEG and the CaCtEG processes

16

Figure 14. Comparison of the IRR of the CtEG and the CaCtEG processes

17 18

Tables

19

Table 1. Basic properties of raw coal (From Holingola city, China)

20

Table 2. Kinetic parameters of DMO hydrogenation reaction

21

Table 3. Benchmark case for calculation of investments

22

Table 4. Market price of raw material and utilities

23

27



Page 28 of 46

1 2 CO2

Coal

CG

WGS

O2

Air

ASU

GSP

H2

EG EGS

EGR

DMO

unshifted gas

O2 N2

CO

DMOS

CH3OH

3 4

Figure 1. Schematic diagram of the conventional CtEG process

28


Page 29 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1 COG CH4 DMR

COGS H2 CO2 CO2

Coal

EG CG

WGS

GSP

O2

unshifted gas

2 3

ASU

EGR

DMO

O2 Air

EGS

N2

CO

DMOS

Figure 2. Schematic diagram the novel CaCtEG process

4

29


CH3OH

Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

COG

Compressors

2

Page 30 of 46

Desulfurization reactors

CO2 emission 10

H2

H2 Coal

DMR reactor

PSA

1

CO2 Absorber

Mill

CH4

Screen

9

CO2 Water Scrubber

Raw Syngas

11 HP Steam

H2S

H2S Absorber

4

HTS

3

Gasifier & Cooler Radiant

PSA

Ammonia 8

O2

Syngas Flash

COS Reactor

Dry gas

Flyash & Water

Convective Cooler Water

Regenerator Solvent Flash

N2

LP Steam

Water & Slag

Tail gas

Clean Syngas

LTS

CO/N 2 separator

Water H2S Laden Methanol

Solvent Flash

Methanol

6 Recycle gas

H2

5 Tail gas

Methanol (reused)

Methanol

EG recovery column

Separators

DMC Condenser

Methanol (reused)

DMO EGS reactor

H 2O MN regenerator

Methanol recovery column

DMOS reactor

EG 7

DMC DMC DMO column atmospheric column pressurized colum

Methanol recovery column

Figure 3. Simplified flowsheet of the CaCtEG process

30


Dehydration column

EG product column

Page 31 of 46

1 2 3

Elementary efficiency of carbon (EC,%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4 5

3.5 3 2.5 2 1.5 1 0.5 0 0.5

0.4

0.3 αCO

0.2

0.1

0

0

0.1

0.2

0.3

COG/Coal (t/t)

Figure 4. H/C ratio as different COG/Coal and αCO

6 7

31


0.4

0.5


1 2

0.5 Elementary efficiency of carbon (EC,%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 46

0.45 0.4 0.35 0.3 0.25 0.2

0.8

0.6 αCO

3 4

0.4

0.2

0

0

0.2

0.4

0.6

0.8

COG/Coal (t/t)

Figure 5. Elementary efficiency of carbon as different COG/Coal and αCO

5

32


1

Page 33 of 46

1 2 3 100

100 90 80

CO selectivity (%)

CH4 conversion (%)

95 90 85 CH4/CO2=2:1 CH4/CO2=3:2

80 75 70

70 60 50 40 30

CH4/CO2=1:1

20

CH4/CO2=2:3 CH4/CO2=1:2

10

CH4/CO2=2:1 CH4/CO2=3:2 CH4/CO2=1:1 CH4/CO2=2:3 CH4/CO2=1:2

0

600

700

800 900 1000 Temperature (℃ )

1100

1200

600

700

900

1000

1100

1200

(b) CO selectivity

100

5

95

4.5

90

4

CH4/CO2=1:1

3.5

CH4/CO2=2:3

85

CH4/CO2=2:1 CH4/CO2=3:2

CH4/CO2=1:2

H2/CO

3 80 75

2.5 2

CH4/CO2=2:1

70

1.5

CH4/CO2=3:2

65 60

CH4/CO2=1:1

1

CH4/CO2=2:3

0.5

CH4/CO2=1:2

0

55 600

700

800

900

1000

1100

1200

600

700

800

900

1000

Temperature (℃ )

Temperature (℃ )

(c) H2 selectivity

1

800

Temperature (℃ )

(a) CH4 conversion

H2 selectivity (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(d) H2/CO mole ratio

Figure 6. Effect of CH4/CO2 ratio on the performance of the DMR unit

2 3

33


1100

1200


1 2 120

100 95

100

85

H2 selectivity (%)

CH4 conversion (%)

90

80 75 70 0.05 MPa

65

80

60

40

0.05 MPa

0.1 MPa 60

0.1 MPa 20

1.0 MPa

55

1.0 MPa

5.0 MPa

5.0 MPa 0

50 600

700

800

900

1000

1100

600

1200

700

(a) CH4 conversion

900

1000

1100

1200

(b) CO selectivity

100

5

90

4.5

80

4

1.0 MPa

70

3.5

5.0 MPa

60

3

H2 /CO

0.05 MPa

50

0.1 MPa

2.5 2

40 0.05 MPa

30

1.5

0.1 MPa

20

1

1.0 MPa 10

0.5

5.0 MPa

0

0 600

700

800

900

1000

1100

1200

600

700

Temperature (℃ )

800

900

1000

Temperature (℃ )

(c) H2 selectivity

1

800

Temperature (℃ )

Temperature (℃ )

H2 selectivity (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 46

(d) H2/CO selectivity

Figure 7. Effect of pressure on the performance of the DMR unit

2

34


1100

1200

Page 35 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1 2 waste 2.12 t/h H2 5.66 t/h

DMR unit

waste+lost N2+steam dust H2O+CO2 steam ash 26.40 t/h 0.13 t/h 14.07 t/h 11.53 t/h 38.74 t/h 79.73 t/h

CH4-rich 39.81 t/h

steam 70.83 t/h

syngas II 59.78 t/h coal 118.98 t/h

Pretreatment

dry coal 95.58 t/h

Gasification syngas I unit 224.51 t/h

MN recovery

3

others 59.37 t/h gas 6.69 t/h MN 1.17 t/h

CO2 54.91 t/h

CO2 45.31 t/h

water 78.58 t/h

DMO 202.96 t/h

CH3OH HNO3+NaOH O2 5.79 t/h 33.46 t/h 7.08 t/h

waste+lost 97.39 t/h

Purification & separation unit

shift gas 289.54 t/h

waste 1.26 t/h

CO 116.45 t/h

DMO systhesis

COG 47.59 t/h

waste+lost fuel gas 2.50 t/h 7.62 t/h

Water gas shift unit

CO2 water O2 N2 air+CO2 fuel gas 5.50 t/h 8.90 t/h 2.80 t/h 51.00 t/h 29.53 t/h 175.40 t/h waste 5.52 t/h

COGS unit

DMO hydrogenation

CH3OH 105.07 t/h

CH3OH water N2 33.75 t/h 0.11 t/h 8.16 t/h H2 15. 54t/h

crude EG 112.17 t/h

N2 7.99 t/h

4 5

Figure 8. Mass balance of the whole CaCtEG process

6

35


EG refining

EG product 103.05 t/h

others waste 9.84 t/h 7.27 t/h


Page 36 of 46

EGS

2506 kmol ·C/h

2185 kmol ·C/h

1878 kmol ·C/h

321 kmol ·C/h 5737 kmol ·C/h

CG

3700 kmol ·C/h

WGS

1515 kmol ·C/h

GSP

DMOS

1207 kmol ·C/h

90 kmol ·C/h

2416 kmol ·C/h

EGR

1210 kmol ·C/h

105 kmol ·C/h

2037 kmol ·C/h

(a) CtEG process

1 1680 kmol ·C/h

DMR

2928 kmol ·C/h

5737 kmol ·C/h

CG

3700 kmol ·C/h

1680 kmol ·C/h

COGS

EGS

1030 kmol ·C/h

1248 kmol ·C/h

WGS

6628 kmol ·C/h

GSP

4706 kmol ·C/h

2 3

2037 kmol ·C/h

4350 kmol ·C/h


DMOS

287 kmol ·C/h (b) CaCtEG process

Figure 9. Equivalent carbon balance of the CtEG and the CaCtEG processes

36


3283 kmol ·C/h


EGR

3324 kmol ·C/h

Page 37 of 46

1 45

3.0 EC CO2

2.5

35 30

2.0

25 1.5 20 15

1.0

CO2 emission (t/t-EG)

40

EC (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


10 0.5 5 0

2 3

0.0 CtEG

CaCtEG

Figure 10. Carbon utilization efficiency of the CtEG and the CaCtEG processes

4

37



Page 38 of 46

1 2 others 10.89%

others 14.67% product 30.68%

product 41.27%

destructi on 47.84%

destructi on 54.65%

(a) CtEG process

1

(b) CaCtEG process

Figure 11. Exergy analysis of the CtEG and the CaCtEG processes

2

38


Page 39 of 46

1 20000

Working capital and contingency

18000 total capital investment (CNY/t-EG)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Construction and contractor fee

16000

Engineering and supervision

14000

Buildings and land

12000

Instruments, piping and electrical

10000

Equipment and installation

8000 6000 4000 2000 0 CtEG

CaCtEG

2 3

Figure 12. Distribution of the TCI of the CtEG and the CaCtEG processes

4 5

39



1 2 5500 Gereral expenses

5000 total product cost (CNY/t/y)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Plant overhead costs

4500

Fixed charges

4000 3500

Operating & Maintenance

3000

Utilities

2500

Raw material

2000 1500 1000 500 0 CtEG

3 4

CaCtEG

Figure 13. Distribution of the TPC of the CtEG and the CaCtEG processes

40


Page 40 of 46

Page 41 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1 2 20.0% 18.0% 16.0% 14.0% 12.0% 10.0% 8.0% 6.0% 4.0% 2.0% 0.0%

3 4

CtEG

CaCtEG

Figure 14. Comparison of the IRR of the CtEG and the CaCtEG processes

5

41



Page 42 of 46

1 2 3 4

Table 1. Basic properties of raw coal (From Holingola city, China) proximate analysis (wt. %)

elementary analysis (wt. %, dry-basis)

moisture

28.4

carbon

75.82

fixed carbon

57.86

hydrogen

5.54

volatile matter

35.14

nitrogen

1.17

ash

21.97

sulfur

0.60

LHV

16.82 (MJ/kg)

oxygen

13.36

5 6

42


Page 43 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1 2 3

Table 2. Kinetic parameters of DMO hydrogenation reaction parameter name reaction constant

rate

expression

k1 =5.95 × 1016exp（-1.49 × 105 /RT)

k 2 =4.76 × 1023exp（-2.10 × 105 /RT)

k3 =6.79 ×1024exp（-2.38 ×105 /RT) reaction equilibrium constant

KDMO =1.31 ×10-4exp（4.29 ×104 / RT)

KCH3OH =3.80 ×10-6exp（5.63 ×104 /RT)

K MG =4.86 × 10-3exp（2.72 × 104 /RT)

K EG =7.20 × 10-2exp（1.81 × 104 /RT)

KET =8.22 ×10-3exp（2.52 ×104 /RT)

K p1 =5.58 ×10-5exp（6.56 ×104 /RT)

K p 2 =1.07 ×10-4exp（4.10 ×104 /RT)

4

43



1

2 3

Page 44 of 46

Table 3. Benchmark case for calculation of investments Iθ (108 CNY)

unit

benchmark

θ

ASU

oxygen supply

0.50

21.3 kg/s

2.83 a

CG

daily coal input

0.65

39.2 kg/s

5.84 b

WGS

material caloric value

0.67

1450 MW

2.46 c

GSP

shift syngas input

0.65

6778 kmol/h

5.49 d

EGS

DMO input

0.65

74.21 t/h

4.86 e

EGR

EG output

0.65

37.50 t/h

5.27 e

DMOS

H2 input

0.65

2845.50 kmol/h

3.45 e

DMR

mixed gas to reforming

0.80

33451 kmol/h

3.15 f

PSA

H2 input

0.50

21.3 kg/s

2.87 f

Qθ

a: Man et al., 2014; b: Xiang et al., 2016; c: Yang et al., 2012; d: Qian et al., 2015; e: Yang et al., 2017; f: Yi et al., 2017.

4 5

44


Page 45 of 46 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1 2

Table 4. Market price of raw material and utilities items

price

items

price

raw coal

500 (CNY/t)

NH3·H2O

2850 (CNY/t)

3

COG

0.6 (CNY/m )

NaOH

4230 (CNY/t)

CH3OH

2845 (CNY/t)

NaNO2

2850 (CNY/t)

HNO3

1500 (CNY/t)

Heating cost

36.89 (CNY/GJ)

electricity

0.67 (CNY/kWh)

Water

2.85 (CNY/m3)

3

45



Table of Contents graphic

1 2

46


Page 46 of 46

Development of a coke oven gas assisted coal to ethylene glycol

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