l-

n 40,

S.0%.

Present strengths and weaknesses of the CTO compared to the methanol-to-olens.

a r t i c l e i n f o a b s t r a c t

proached to 57% in 2012. Thus, development of the coal-based ole-ns industry is favorable in the context of increasingly severe oilsupply shortage. There are now three coal-to-olens (CTO) projects

to CO2 mitd as geolo

2 capture anage (CCS) technology has received increasing attention bof its large capacity of reducing CO2 emissions. It is a monomical and efcient method compared to developing renewableenergy, retrotting major equipments, and improving energy inte-gration for resource and energy saving [5].

A CCS process in general involves three stages: separating CO2from ue gas, compressing CO2 for pipeline transport, and inject-ing CO2 into geologic reservoirs. For carbon capture, there aremainly three technologies developed, including post-combustioncapture, oxy-fuel combustion capture, and pre-combustion

Corresponding author. Address: Center for Process Systems Engineering, Schoolof Chemical Engineering, South China University of Technology, Guangzhou510640, PR China. Tel.: +86 20 87113046, +86 13802902300.

E-mail address: ceyuqian@scut.edu.cn (Y. Qian).URL: http://www2.scut.edu.cn/ce/pse/qianyuen.htm (Y. Qian).

Chemical Engineering Journal 240 (2014) 4554

Contents lists availab

Chemical Engine

journal homepage: www.1 Dong Xiang and Siyu Yang contributed equally to this paper.sources. From 2005 to 2011, coal accounted for 75.1% of the totalenergy production of China, oil for 15.2%, and natural gas for2.8%, as shown in Fig. 1. The oil import dependence was ap-

duction of urea and methanol, their contributionis nite. Physical methods are generally regardestoring CO underneath. In recent years, carbon1385-8947/$ - see front matter 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.cej.2013.11.051igationgicallyd stor-ecausere eco-1. Introduction

As the backbone of the petrochemical industry, olens produc-tion scale is critical to development of national economy. As moreand more oil-to-olens projects launched in China, the productiongrows quickly, and the self-sufcient rate of ethylene and propyl-ene will increases up to 53% and 74% by 2015 [1]. However, thereis still a big gap between the domestic supply and demand, whichis in urgently needed to be lled by olens based on alternative re-

under operation and other two CTO projects in plan in the nextthere years in China. These installations are going to approach acapacity of 3 Mt/y [3].

However, CTO is facing the problem of high CO2 emissions.There have been a number of techniques of CO2 mitigation devel-oped from chemical and physical methods [4]. For chemical meth-ods, CO2 is reused mostly as feedstock to produce valued chemicalproducts. Although these methods enable us to exploit CO2 as avaluable feedstock in many different applications such as the pro-Article history:Received 5 September 2013Received in revised form 21 November 2013Accepted 23 November 2013Available online 28 November 2013

Keywords:Energy efciencyCostCoal-to-olensCCSMethanol-to-olensCoal-to-olens (CTO) has been attracting more attention of the chemical process industry, in the light ofthe scarcity of oil resources and richness of coal in China. However, it is inherently accompanied with theproblem of severe greenhouse gas emissions. CTO processes therefore face increasing challenges fromother alternative processes, especially methanol-to-olens (MTO) process. This paper conducts a detailedtechno-economic analysis of the CTO process with CCS. The effect of carbon capture is studied. The CTOprocess with 80% carbon capture is slightly less thermodynamically efcient than the conventional CTOprocess. The corresponding mitigation cost of the process is 150 RMB/t, which is roughly equivalent tothe current carbon price. Thus, the effect of energetic and economic penalties on this carbon capture con-guration is negligible. In comparison to the MTO process, the CTO process with CCS is competitive inproduct cost even considering carbon tax and it is capable of resisting to market risk. CTO processes withappropriate CO2 reduction are more applicable to olens industry in China.

2013 Elsevier B.V. All rights reserved.Techno-economic performance of the coa

Dong Xiang 1, Siyu Yang 1, Xia Liu, Zihao Mai, Yu QiaSchool of Chemical Engineering, South China University of Technology, Guangzhou 5106

h i g h l i g h t s

Conduct a techno-economic analysis of the coal-to-olens (CTO) with CC Analyze effects of key factors on the CTO with appropriate capture rate 8to-olens process with CCS

PR China

le at ScienceDirect

ering Journal

elsevier .com/locate /cej

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

CCS carbon capture and storage

C plant overhead cost (RMB/t)

RFi ratio factor of component i (%)Sj practical scale of unit jSrJ reference scale of unit jsf scale factorTCI total capital investment (RMB/t/y)

1000

1500

2000

2500

3000

3500

Mt

Hydro,Nuclear,WindNatural gasCrude oilCoal

eericapture [6]. These technologies are usually applied in pulverized-coal power plants and some chemical plants [7]. Introducing aCCS will bring penalties on both energetic and economic perfor-mance [810]. For example, in most coal-based power plants, theCO2 avoidance cost is about 250330 RMB/t, which is muchhigher than the current carbon price. The penalties brought bythe CCS on chemical processes is, however, lower than thoseon power generation processes [11,12]. It demonstrates that itis necessary to assess the impact of CCS on the whole perfor-mance of CTO processes.

CG coal gasicationCTO coal-to-olensLHV lower heating valueMS methanol synthesisMTO methanol-to-olensRMB ren min biWGS water gas shift

Notations in formulationh domestic-made factorCAC administrative cost (RMB/t)CCF cumulative cash ow (RMB)CCR carbon capture rate (%)CD depreciation cost (RMB/t)CDSC distribution and selling cost (RMB/t)CFi cash ow of year i (RMB)CO&M operating & maintenance cost (RMB/t)Nomenclature

AbbreviationsAGR acid gas removalASU air separation unit

46 D. Xiang et al. / Chemical EnginPlanning a sound development roadmap for alternative olensproduction requires a broad and comprehensive assessment. Tech-no-economic analysis is an essential part of this process. Moreimportantly, the role of CCS in CTO development is needed to beanalyzed to nd the trade-off among environmental protection, en-ergy penalty, and economic performance. There have been somestudies on techno-economic analysis of CTO processes [1318].However, the literatures on analyzing CTO processes with CCS fromtechno-economic point of view could not be found. Besides, someviews back up developing methanol-to-olens (MTO) processessince they have the advantages of low capital investment and envi-ronmental impact. There are now 1 MTO project under operationand other 10 MTO projects in plan in the next three years in China,which will approach to a capacity of 6.8 Mt/y [3]. With the poten-tial challenge of the MTO process, how should people congureCCS on the CTO process? We answer this question by the techno-economic comparison of the CTO process with CCS and the MTOprocess in this paper.

2. Process modeling

As a base of techno-economic analysis, major units of a CTOprocess are modeled, including an air separation unit (ASU), a coalgasication unit (CG), an acid gas removal unit (AGR), a carboncapture and storage unit (CCS), a water gas shift unit (WGS), amethanol synthesis unit (MS), and a methanol-to-olens unit(MTO). For a plant with given capacity and specied operating con-ditions, the model calculates all mass and energy ows. The detailsof the modeling are described in the following sections.POC

CR raw material cost (RMB/t)CTS&M cost of CO2 transportation, sequestration and monitor-

ing (RMB/t)CU utilities cost (RMB/t)EI equipment investment (RMB)EIrJ reference equipment investment of unit j (RMB)EwCCS quantity of CO2 emitted from the CTO plant with CCS

(Mt/y)Ew/oCCS quantity of CO2 emitted from the CTO plant without CCS

(Mt/y)MC mitigation cost (RMB/t)OP olens price (RMB/t)OYi olens yield (Mt/y)PC product cost (RMB/t)PCw CCS product cost of the CTO plant with CCS (RMB/t)PCw/o CCS product cost of the CTO plant without CCS (RMB/t)ng Journal 240 (2014) 45542.1. Coal-to-olens process

The ow diagram of the CTO process, including the MTO pro-cess, is shown in Fig. 2. Coal and water are gasied with the oxygenagent from the ASU, to produce syngas in the CG. The hot syngas isquenched in a radiant cooler and a convection condenser, whereheat is recovered to generate steam. The syngas is then fed intothe WGS to increase the ratio of H2/CO for the methanol synthesis.Before methanol synthesis, the syngas is cleaned in the AGR to re-move H2S and CO2. The clean syngas is then sent to the MS to pro-duce methanol. The crude methanol solution is concentrated to90% (moral fraction) before fed into the MTO. Prior to olens sep-aration, there are a serial of steps: quenching, washing, drying, andcompression. The front-end depropanization separation techniqueis applied to separate olens into ethylene and propylene [18].

2.1.1. Coal gasication unitIn the CG, Texaco gasication technique was adopted. For mod-

eling, coal is rstly divided into three kinds of nonconventionalmatter as coke, ash, and unburned carbon. Then nonconventionalmatter is decomposed in RYield model in Aspen Plus by element

0

500

1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010Year

Fig. 1. Prole of major energy production in China [2].

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

Mill

Water

Screen

Coal

Raw syngas

Water

ater

Water

wat

WGS reactor

Oxygen from ASU

D. Xiang et al. / Chemical EngineeriWater & slag

Gasifier&

CoolerRadiant Water

Steam

Convective Cooler

Steam

Purge gas

Lurgimethanolreactor

Methanol

Methanol

Unreacted gas

DMTOreactor

W

Clean syngas

Waste

analysis [19]. After this, decomposed components, O2, water, etc.are all fed into RGibbs reactor, which calculates chemical equilib-rium by Gibbs energy minimization. The composition of gaseousmix was determined according to the property of the input coalas shown in Table 1. The simulation was veried by comparingthe composition of the output syngas with that of Zheng and Furin-skys work [21]. The simulated composition is similar to the refer-ence composition with only a small relative error less than 1.5%[22].

2.1.2. Methanol synthesis unitFor modeling of methanol synthesis, Lurgi synthesis reactor was

used and modeled by using the Requil model in Aspen Plus. In gen-eral, there are several major reversible reactions in the methanolsynthesis reactor. CuZnAl catalyst was used for this reactionwith its suitable temperature 513 K and pressure 8.2 MPa [22,23]. The main reactions are shown in Eqs. (1 and 2):

CO 2H2 ! CH3OH 1

Crude methanol

Bottom liquid

Pressure distillation

column

Atmospheric distillation

column

Deprop

Fig. 2. Process ow diagra

Table 1Properties of coal in Yanzhou, China [20].

Proximate analysis (wt.%) Ultimate analysis (wt.%, dry)

Moisture content 5.81 Ash 7.53Fixed carbon 49.85 Carbon 73.64Volatile matter 37.24 Hydrogen 5.24Ash 7.10 Nitrogen 1.13

Sulfur 2.63Oxygen 9.83Scrubber

Regenerator

Methanol

Tail gas

H2S

Air

S

Tail gas

Quenchingtower

Alkaline towerWater

scrubberWaste water

Dryer

WaterWater

NaOH

EthyleneFuel gas Propylene

Acid gas absorber

N2

H2S concentration tower

er

ng Journal 240 (2014) 4554 47CO2 3H2 ! CH3OHH2O 2The raw syngas from the CG is cleaned in the AGR presented in

the CCS and then shifted into syngas with the molar ratio betweenhydrogen and carbon monoxide of about 2 [24]. The clean syngas isput into the MS as the feedstock. Following the synthesis reaction,the unreacted syngas are separated out from the chemical productsand recycled back to the MS to increase the methanol production[6]. RadFrac model was used to simulate the separation columnsand Peng-Rob was selected as the thermodynamic method. Detailsof the simulation refer to the authors previous work [22].

2.1.3. Methanol-to-olens unitMethanol with molar fraction 90% is converted into product gas

in MTO reactor. The hot product gas is cooled in the quenchingtower and cleaned in the alkaline tower with NaOH solution to re-move H2S and CO2. After then, ethylene and propylene are ex-tracted by the front-end depropanization seperation technique.DMTO technique was used to synthesize olens. The main reac-tions in the synthesis reactor could be summarized as follow:

2CH3OH! C2H4 2H2O 3

3CH3OH! C3H6 3H2O 4

4CH3OH! C4H8 4H2O 5An attrition resistant SAPO-34 was employed as the catalyst.

According to the specication of the catalyst, the temperatureand pressure were xed at 763 K and pressure 0.22 MPa. In thiscondition, the methanol conversion has reported to be close to

C2 splitter

C4=

PropaneEthane

C3 splitter

anizer Demethanizer Dethanizer

m of the CTO process.

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

AnitaHighlight

100%. The olens synthesis was modeled by Rstoic model in AspenPlus. The composition of product gas was calculated according tothe Ref. [25]. RadFrac model was used to simulate rectifying col-umns. The process compressors were modeled by assuming com-mon isentropic and mechanical efciency. The NRTL, ELECNRTL,and RKS-BM were adopted as the thermodynamic methods ofwater scrubber, alkaline tower, and separation tower, respectively.Details of the simulation referred to the authors previous work[18,26].

2.2. Carbon capture and storage process

The CCS includes carbon capture, compression, transportation,and storage. The process ow diagram is shown in Fig. 3. The crudesyngas from the gasifer consists of impurities that are mainly ashand acid gases. It is necessary to remove these impurities beforemethanol synthesis. We employed Rectisol method in this paper.The syngas from the WGS is fed into the water scrubber to removeammonia and y ash. After ash dehydration, it is fed into the bot-tom of the acid gas absorber and absorbed by top-down low tem-perature methanol, which is obtained from the regeneration towerand cooled through multistage cooling to 223 K. The upper part ofthe absorber mainly removes CO2 while the lower part removes

to transport CO2 in our model. Puried CO2 is rstly compressed to15 MPa and then transported to and injected into undergroundreservoirs. 20 km for transportation distance and the saline aquiferat 2 km deep as the geological position of the reservoirs wasconducted.

3. Analysis methodology

In this section, we mainly analyze the CTO process with CCSfrom technical and economic points of view. A few indexes are se-lected involving energy efciency, capital investment, product cost,and cumulative cash ow.

The energy efciency is dened as the product energy gener-ated by all input energy, as shown in Eq. (6). The energy of coal,methanol, and olens is calculated based on their lower heatingvalues. The all input energy involves both the energy of feedstockand utilities.

Energy efficiency Product energyMWAll input energyMW 6

Another technical factor is carbon capture rate (CCR) which isdened as the mass ow of captured CO2 divided by CO2 emissions,as shown in Eq. (7).

48 D. Xiang et al. / Chemical Engineering Journal 240 (2014) 4554sulfur containing compounds. Without CO2 capture process, CO2is separated and exhausted to environment by using N2 as thestripping gas. In this case, the exhausted gas is a mixture of N2and CO2. For CO2 capture process, a desorber and a companyingash are introduced to purify CO2 to the high concentration ofabout 98%. The capture rate of CO2 could be increased by changingthe temperature and pressure of the ash. The H2S separated frommethanol regenerator is placed into CLAUS conversion process forsulfur recovery.

For modeling, RadFrac model was used to simulate the acid gasabsorber, the desorber, the H2S concentration tower, and theregenerator. Flash model and Compr model were adopted for sim-ulating ashes and compressors, respectively. PSRK was selected asthe thermodynamic method. The described CCS referred to the CCSdemonstration of coal-to-liquild process installed by Shenhuagroup in Ordos, China [27]. Different from this CCS, we use pipeline

Waste water

Acid gas absorber

Clean syngas

Crude syngas

Water

CO2

Water scrubberFig. 3. Process ow diagraCO2 transport(Pipeline)

CO2 storage(Saline acquifer)CCR Captured CO2 mass flow Mt=yCO2 emissions Mt=y 7

For economic indexes, the capital invested for manufacturingand plant facilities is dened as the xed capital investment, whilethose for the plant operation is dened as the working capital. Thesum of the xed capital investment and the working capital is de-ned as the total capital investment. In order to evaluate these in-dexes of olens production processes, it is necessary to know thecapital investment of the basic equipments of the CTO process thatcould be calculated according to the benchmark case shown in Ta-ble 2. The detailed calculation of these equipments follows Eq. (8).While the equipment investment of CO2 transportation and storagewas calculated by the Ref. [30]. The other components of the totalcapital investment could be determined according to their ratios to

Regenerator

Methanol

Tail gas

H2S

Air

S

Tail gas

H2S concentrationtower

Desorber

N2m of the CCS process.

AnitaHighlight

AnitaHighlight

the equipment investment. The ratios are shown in Table 3 and thecalculation follows Eq. (9) [3133]. In this paper, the capital invest-ment was updated to 2012 prices by using the Chemical Engineer-ing Plant Cost Index [34,35]. The currency exchange rate betweenUS$ and RMB was 6.2 in 2012 and the olens price was set to be10,000 RMB/t [36].

EI XJ

h EIrj SjSrj

!sf8

Cumulative cash ow was calculated by adding all of the cashows from the inception of projects, as shown in simplied Eq.(12). As project life, 23 years was used in this paper, of which3 years for plant construction and 20 years for operation. Assump-tions were made for construction phase that the expenditure factorwas 80% for the rst 2 years and 20% for the last year [37].

CCF Xi

CFi Xi

OP PC CDi OYi 12

where CCF is the cumulative cash ow, CFi is the cash ow of year i,OP is the olens price, PC is the product cost, CD is the depreciationcost, OYi is the olens yield of year i.

Size factor (sf) Domestic-made factor (h) EIrJ (M$) Refs.

0.50 0.50 45.70 [22]0.67 0.65 29.10 [22]0.67 0.80 78.00 [22]0.67 0.65 39.80 [28]0.67 0.65 67.30 [28]0.67 0.65 32.80 [28]

Table 3Ratio factors for capital investment.

Component Ratio factor (RF, %)

(1) Direct investment(1.1) Equipment 100(1.2) Installation 48(1.3) Instruments and controls 24(1.4) Piping 57(1.5) Electrical 29(1.6) Buildings(including services) 71

t(2) Utilities Water 2 RMB/t, electricity 0.7 RMB/kWh,

steam 42 RMB/GJ(3) Operating & Maintenance(3.1) Operating labor CTO 300 labors, MTO 100 labors, 100,000

RMB/labor/year(3.2) Direct supervisory and

clerical labor20% of operating labor

(3.3) Maintenance and repairs 2% of xed capital investment(3.4) Operating supplies 0.7% of xed capital investment(3.5) Laboratory charge 15% of operating labor(4) Depreciation Life period 20y, salvage value 4%(5) Plant overhead cost 60% (3.1 + 3.2 + 3.3)(6) Administrative cost 2% of product cost(7) Distribution and selling

cost2% of product cost

(8) CO2 TS&M 64 RMB/t CO2(9) Product cost (1) + (2) + (3) + (4) + (5) + (6) + (7) + (8)

D. Xiang et al. / Chemical Engineering Journal 240 (2014) 4554 49TCI EI 1Xi

RFi

!9

where EI is the equipment investment, h is the domestic-made fac-tor, EIrj is the reference equipment investment of unit j, Sj is thepractical scale of unit j, Srj is the reference scale of unit j, sf is thescale factor, TCI is the total capital investment, RFi is the ratio factorof capital investment of component i.

For calculation of the product cost, we made some assumptionsas listed in Table 4. The consumption of raw materials and utilitieswas determined according to simulation results. Their correspond-ing costs were calculated on the basis of the average prices of 2012in China [18]. Operating labor cost was calculated referring toHans work [13]. A straight-line method was adopted to calculatethe depreciation cost under the assumption of 20 years life timeand 4% salvage value. CO2 TS&M cost was calculated by Mantri-pragada and Rubins work [11]. The rest part of product cost wascalculated according to the ratio to product cost [31,32]. The prod-uct cost is dened as the sum of the above components as shown inEq. (10).

PC CR CU CO&M CD CPOC CAC CDSC CTS&M 10where PC is the product cost, CR is the raw material cost, CU is theutilities cost, CO&M is the operating & maintenance cost, CD is thedepreciation cost, CPOC is the plant overhead cost, CAC is the admin-istrative cost, CDSC is the distribution and selling cost, CTS&M is thecost of CO2 transportation, sequestration, and monitoring.

The cost related to CO2 emissions reduction should also be con-sidered during product cost estimation. In this paper, we used mit-igation cost (MC) to evaluate the cost according to Refs. [37,38]. MCrepresents the difference of cost per ton of CO2 emissions avoidedbetween the plant without CCS and the plant with CCS expressedin Eq. (11).

MC PCwCCS PCw=oCCSEw=oCCS EwCCS 11

where PC is the product cost of the CTO plant, E is the quantity ofCO2 emitted from the CTO plant, the subscripts w CCS and w/oCCS are referred to the plant congurations with and without CCS.

Besides the capital investment and the product cost, there is an-other important economic factor-plant cash ow. It is usually con-sidered as the cumulative ow over the life of the project.

Table 2Summary of investment data for main equipment components.

Unit Benchmark Scale (SrJ )

ASU Oxygen supply 21.3 kg/sCoal handing Daily coal input 27.4 kg/sCG Daily coal input 39.2 kg/sWGS Material caloric value 1377 MWAGR Sulfur output 29.3 mol/s

Pure CO2 captured 2064.4 mol/s

MS Syngas input 10,810 mol/s 0.67MTO Methanol input 62.5 kg/s 0.60(1.7) Land 5(2) Indirect investment(2.1) Engineering and supervision 48(2.2) Construction expenses 43(2.3) Contractors fee 19(2.4) Contingency 33(3) Fixed capital investment 477(4) Working capital 80(5) Total capital investment 557

Table 4Assumptions for the estimation of product cost.

Component Basis

(1) Coal Coal price 620 RMB/t; methanol 2,400 RMB/0.65 20.40 [22]1.00 223.06 [29]

4. Results and discussion

This section reports the mass and energy data as well as com-pares the different cases of CTO processes with CCR ranging from60% to 95%. A MTO process is also involved in this comparison,aiming to get which alternative olens production should be devel-oped in large-scale. In the end of this section, we analyze threeimportant parameters, plant scale, carbon tax, feedstock price tond their effects on economic performance.

4.1. Energy efciency analysis

The CTO plant with CCS and the MTO plant producing the same0.7 Mt/y olens were simulated in Aspen Plus, which produce allprocess data needed to assess the techno-economic and environ-mental performance of cases studied. As an illustrative examplefor mass and energy balance, Table 5 presents the main streamproperties in key points of the CTO plant diagram, and Table 6 pre-sents properties of N2 stream, CO2 stream, and tail gas stream ofCCS at CCR 60%, 80%, and 95%. The properties of shift syngas streamand clean syngas stream of CCS can be found in Table 5.

The total material and energy consumption of MTO and CTOplants at different CCRs is shown in Table 7. The energy consump-tions or generations of ASU, CG, WGS, CCS, MS, and MTO are alsoplaced in this table. Producing 0.7 Mt/y of olens needs about1.8 Mt/y methanol for the MTO plant and 2.87 Mt/y coal for theCTO plant. The resulting CO2 emissions of the CTO plant are closeto 4.05 Mt/y. The energy efciency to olens product in Table 5is calculated according to Eq. (6). With shorter conversion route,

and 80%. The corresponding energy efciency ranges from 35.86%to 35.69% since the electricity consumption changes from172.54 MW to 187.58 MW. In the second scenario, the CTO processhas a high CCR between 80% and 95%. The corresponding energyefciency ranges from 35.69% to 35.38% since the electricity con-sumption changes from 187.58 MW to 215.93 MW. It is clear thatthe increasing rate of electricity consumption of CCS in the secondscenario is about 2 times larger than that in the rst scenarioshown in Fig. 4. The decrease of energy efciency is caused bythe increase of electricity consumption of the CCS. On the onehand, we should raise the ash temperature and reduce the ashpressure in order to increase CCR and cool the methanol out ofthe ash to 223 K for recycling use. Correspondingly, the increas-ingly temperature difference leads to bigger ammonia cold energyconsumption when CCR changing from 60% to 95%. On the otherhand, with increasing CCR, CO2 processing capacity and the com-pression energy consumption increase linearly, as shown in Fig. 4.

4.2. Economic analysis

4.2.1. Capital investment, product cost, and cumulative cash owThe breakdown of total capital investment of CTO plants is

shown in Fig. 5. The MTO takes 45.6% of the total capital invest-ment, followed by the ASU and CG (about 37.3%). It is seen thatadditional investment for CCS makes the total capital investmentincrease from 2.52 104 RMB/t/y to 2.71 104 RMB/t/y whenCCR is as high as 95%.

On the other hand, the product cost of MTO and CTO plants arecalculated and shown in Fig. 6. For the CTO plant, most of capital is

)

0

67.10 3.46 0.01 0.06

70

50 D. Xiang et al. / Chemical Engineering Journal 240 (2014) 4554the energy efciency of the MTO plant is around 80.98%, muchhigher than that of the CTO plant which is only 36.16%.

CTO processes with CCS have two scenarios divided by CCR 80%.In the rst scenario, the CTO process has a low CCR between 60%

Table 5Simulation results of main streams in the CTO process.

Streama Coal (1) Water(2)

Oxygen(3)

Syngas(4)

Shiftsyngas(5)

N2 (6

Molar fraction (%)N2 1.39 0.87 0.85 100.0O2 95.00 AR 3.61 1.03 0.98 H2O 100.00 19.07 01.61 CO 40.47 18.71 CO2 11.67 31.56 H2S 0.34 0.32 H2 26.55 45.97 C CH4 CH3OH C2H6 C2H4 C3H8 C3H6 C4H10 C4H8 C4H6 C5H12 Molar ow

(kmol/hr) 10,708 10,358 36,359 37,676 4893

Mass ow(kg/hr)

358,295 192,926 333,886 771,303 794,423 137,0

Temperature(K)

314 314 383 425 363 293

Pressure(Mpa)

0.1 0.1 4.1 2.76 5.00 0.2

Enthalpy 1128.52 842.74 6.58 1347.27 1535.44 0.22

(MW)

a In order to simplify the table, some minor streams are not included, such as water 1.02 67.44 0.44 3.16 1.11 0.02 89.70 0.12 0.25 0.18 13.75 99.82 0.57 0.74 0.38 8.90 3.50 99.62 0.04 2.56 1.63 92.61 0.21 0.38 0.38 16,410 25,433 8017 11,002 148 1499 883

633,439 283,069 245,440 245,440 8253 42,064 37,184

302 302 318 763 326 182 315

0.2 2.78 0.40 0.22 0.55 0.20 1.73

1206.44 308.34 542.73 463.06 0.30 19.74 4.68expended on purchasing coal, accounting for 39.5% of the productcost. The second largest is the cost for utilities, about 24.8% of theproduct cost. The total capital investment is involved in the prod-uct cost as the form of depreciation, amounting to 16.8% of the

Tail gas(7)

Cleansyngas(8)

Methanol(9)

Productgas (10)

C4=(11)

Ethylene(12)

Propylene(13)

30.21 1.00 0.11 0.99 0.81 10.18 69.59 0.66 27.29 & slag stream in CG unit, S stream in AGR unit, and purge gas stream in MS unit.

eeriTable 6Simulation results of CCS at CCR 60%, 80%, and 95%.

D. Xiang et al. / Chemical Enginproduct cost, which is the next major contributor to product cost.By introducing the CCS process, a large amount of CO2 is mitigated,ranging from 7360 t/d to 11,660 t/d.

However, there is additional cost required for CCS energy use,geological sequestration, and monitoring. For the scenario with

Stream CCR 60% CCR 80%

N2 CO2 Tail gas N2

Molar fraction (%)N2 100.00 0.04 34.93 100.00AR 0.02 2.34 CO 0.75 0.82 CO2 98.50 60.18 H2 0.69 1.73 CH3OH 0.03 Mole ow (kmol/hr) 2350 6958 6909 1478Mass ow (kg/hr) 65,832 303,295 258,877 27,397Temperature (K) 293 293 302 293Pressure (Mpa) 0.2 15 0.2 0.2Enthalpy (MW) 0.10 773.01 436.40 0.04

Table 7Mass and energy performance results from the techno-economic model for MTO and CTO

Item MTO plant CTO plant with CCS

CCR 0% CCR 60%

InputCoal (Mt/y)/(MW LHV)a 2.87/2800.24 2.87/2800Methanol (Mt/y)/(MW LHV)b 1.80/1250 Net Electricity input (MWe)c 36.61 146.21 172.54Net Steam input (MWth)c 123.98 212.75 212.75ASU (MWe/MWth) 144.57/ 144.57/CG (MWe/MWth) 70.74/ 70.74/WGS (MWe/MWth) /15.10 /15.10AGR or CCS (MWe/MWth) 9.86/26.59 36.19/26.MS (MWe/MWth) 25.91/77.28 25.91/77.MTO (MWe/MWth) 36.61/123.98 36.61/123.98 36.61/123Total energy input (MW) 1410.59 3159.20 3185.53

OutputEthylene (Mt/y)/(MW LHV)b 0.33/538.54 0.33/538.54 0.33/538.Propylene (Mt/y)/(MW LHV)b 0.30/489.57 0.30/489.57 0.30/489.C4=(Mt/y)/(MW LHV)b 0.07/114.24 0.07/114.24 0.07/114.Product energy (MW LHV) 1142.35 1142.35 1142.35CO2 emissions (Mt/y) Negligible 4.05 1.39Energy efciency (%, LHV basis) 80.98 36.16 35.86

a The LHV is based on Ref. [39].b The LHV is based on Ref. [16].c MWe represents the energy of electricity and MWth represents the energy of steam. T

energy.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0

10

20

30

40

50

60

70

80

90

60 65 70 75 80 85 90 95

CO2

emiss

ions

(Mt/y

)

Ener

gy c

onsu

mpt

ion

(MW

)

CCR (%)

Electricity consumption for ammonia coldElectricity consumption for compression CCS electricity consumptionCO2 emissions

Fig. 4. The relationship between CCR and electricity consumption.ng Journal 240 (2014) 4554 51low CCR, the product cost increases from 6911 RMB/t to7131 RMB/t, leading to an increase of 3.2%. For the scenario withhigh CCR, the product cost increases to 7437 RMB/t, leading to anincrease of 7.6%. It is obvious that the big change happens at the

CCR 95%

CO2 Tail gas N2 CO2 Tail gas

0.03 32.12 100.00 0.03 48.980.02 4.98 0.02 17.390.59 1.66 0.54 5.3198.90 57.30 99.00 14.730.43 3.94 0.38 13.590.03 0.03 9255 3240 391 10,984 925404,681 119,068 10,953 480,601 26,715293 302 293 293 30215 0.2 0.2 15 0.2976.51 195.44 0.02 1226.38 14.29

plants at different CCRs.

CCR 70% CCR 80% CCR 90% CCR 95%

.24 2.87/2800.24 2.87/2800.24 2.87/2800.24 2.87/2800.24 179.10 187.58 204.14 215.93212.75 212.75 212.75 212.75144.57/ 144.57/ 144.57/ 144.57/70.74/ 70.74/ 70.74/ 70.74//15.10 /15.10 /15.10 /15.10

59 42.75/26.59 51.23/26.59 67.79/26.59 79.58/26.5928 25.91/77.28 25.91/77.28 25.91/77.28 25.91/77.28.98 36.61/123.98 36.61/123.98 36.61/123.98 36.61/123.98

3192.09 3200.57 3217.13 3228.92

54 0.33/538.54 0.33/538.54 0.33/538.54 0.33/538.5457 0.30/489.57 0.30/489.57 0.30/489.57 0.30/489.5724 0.07/114.24 0.07/114.24 0.07/114.24 0.07/114.24

1142.35 1142.35 1142.35 1142.351.04 0.69 0.35 0.1735.79 35.69 35.50 35.38

he symbol of are used to make a distinction between generated and consumed

0

5

10

15

20

25

30

35

40

0 60 70 80 90 95

Tota

l cap

ital i

nves

tmen

t (10

00 R

MB/

t/y)

CCR (%)

Increase of CCS MTO MSWGS AGR CGASU

Fig. 5. Distribution of total capital investment for CTO plants at different CCRs.

CCS, as shown in Figs. 7 and 4. Thus, CTO with this carbon capture

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

MTO CCR 0% CCR 60% CCR 70% CCR 80% CCR 90% CCR 95%

Prod

uct c

ost (

RMB/

t)

CO2 TS&M Distribution and selling costAdministrative cost Plant overhead costDepreciation Operating & Maintenance

Fig. 6. Distribution of product cost for MTO and CTO plants at different CCRs.

-2000

-1000

0

1000

2000

3000

4000

5000

6000

5 10 15 20 23Cum

ulat

ive

cash

flow

(milli

on R

MB)

Year

CTO without CCS

CTO with CCR 80%

CTO with CCR 95%

MTO

Fig. 8. Cumulative cash ow of MTO and CTO plants at different CCRs.

52 D. Xiang et al. / Chemical Engineering Journal 240 (2014) 4554conguration is appropriate choice for olens production consider-ing energy penalties, economic performance, and environmentalprotection. The product cost of the MTO plant is about7896 RMB/t, which is much higher than that of the CTO plant withCCS. The methanol cost is the biggest part, amounting to 78.1%, fol-lowed by the utilities cost of 6.7% and depreciation cost of 6.0%.

As shown in Fig. 8, the plant with the highest cumulative cashow is the CTO plant without CCS, followed by the ones withCCS and the MTO plant. The cumulative cash ow decreases from5.0 109 RMB to 3.5 109 RMB as CCR increasing from 0% to95%. While the cash ow of the MTO plant is only 2.9 109 RMB.Although the capital investments of CTO plants are about 2 timeslarger than that of MTO plant, the ratio of cumulative cash owto the MTO plant is 1.21.7. In Fig. 8, we could also nd thebreak-even point and the payback period. The payback period isabout 8 y for the plant without CCS, about 9 y for the plant withCCS, and about 7 y for the MTO plant.

4.2.2. Effects of plant scale, carbon tax, and feedstock priceAs discussed above, we select an appropriate CCR equal to 80%

for case study of the effect of production scale, carbon tax, andCCR 80%, which divides CTO plants with CCS into low capture con-guration and high capture conguration. The big change couldalso be found in the mitigation cost and energy consumption offeedstock price on its economic performance.

120

130

140

150

160

170

180

190

60 65 70 75 80 85 90 95

Miti

gatio

n co

st (R

MB/

t CO 2

)

CCR (%)Fig. 7. Relationship between CCR and mitigation cost.As production scale is one of the most important factor for eco-nomic performance, we therefore study the effect of this factor onthe capital investment and the product cost of the CTO plant withCCS. According to the results, it is clear to nd that the capitalinvestment will decrease as the plant capacity varies from0.3 Mt/y to 2.0 Mt/y, as shown in Fig. 9. The total capital invest-ment of a 2.0 Mt/y plant is about 46.8% of a 0.3 Mt/y plant. Sincedepreciation is a important factor, the product cost also decreaseswith increasing plant capacity. However, the production scaleshows less effect on product cost. For example, the product costof a 2.0 Mt/y plant is about 19.3% less than a 0.3 Mt/y plant, asshown in Fig. 10. For the MTO plant, the effect of economies ofscale is relatively small since the capital investment of the MTOplant is less than half of the CTO plant.

As the largest developing country, China is facing increasingcriticism for the largest greenhouse gas emissions. Chinas 12thve-year plan clearly promised that a carbon trading market wouldbe gradually established and CO2 emissions intensity be reduced atthe same time. The city of Shenzhen launched a carbon tradingscheme on 18 June 2013, Chinas rst market for compulsory car-bon trading. The scheme covers 635 industrial companies andsome public buildings accounting for about 40% of the citys emis-sions [40]. This means that there will be an explicit cost associatedwith CO2 emissions in the near future in China.

The effect of increasing carbon tax on the product cost is shownin Fig. 11. It is obvious that when carbon tax exceeds 250 RMB/t

the product cost of the CTO plant without CCS is higher than thatof the MTO plant, while the product cost of the CTO plant with

0

5

10

15

20

25

30

35

40

0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 2.0

Tota

l cap

ital i

nves

tmen

t (10

00RM

B/t/y

)

Capacity (Mt/y)

Incremental investment of CCS

CTO without CCS

Fig. 9. Total capital investment of the CTO plant with CCS varying with differentcapacities.

eeri3000

4000

5000

6000

7000

8000

9000od

uct c

ost (

RMB/

t)

Incremental cost of CCS CTO without CCS

D. Xiang et al. / Chemical EnginCCS is much lower than that of the MTO plant when carbon tax isas high as 400 RMB/t. For the CTO plant with CCS, the break-evencarbon tax between CTO plants with and without CCS is about150 RMB/t, roughly equivalent to the current carbon price. Thus,the CTO plant with CCS could be rstly built to demonstrate thepotential application of CCS technologies from the aspects of envi-ronmental protection and overall economic performance. It isimportant to underline that, if the carbon price increases up to300400 RMB/t in the next few years, the application of CCS tech-nologies for large-scale CTO plants will become very protable.

The effect of feedstock price on product cost of the MTO plant isabout 2 times that of the CTO plants with and without CCS, as

NSF Key Project (No. 21136003), the China NSF Project (No.

0

1000

2000

0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 2.0

Pr

Capacity (Mt/a)Fig. 10. Product cost of the CTO plant with CCS varying with different capacities.

5000

5500

6000

6500

7000

7500

8000

8500

9000

0 30 60 90 120 150 180 210 240 270 300 330 360 400

Prod

uct c

ost (

RMB/

t)

Carbon tax (RMB/t CO2)

CTO without CCS CTO with CCS

MTO

Fig. 11. Effect of carbon tax on product cost.

3000

5000

7000

9000

11000

13000

15000

Prod

uct c

ost (

RMB/

t)

Coal price/methanol price (RMB/t)

CTO without CCS CTO with CCS

MTO

200/800 400/1600 600/2400 800/3200 1000/4000 1200/4800

Fig. 12. Effect of prices of feedstock on product cost.21306056), the National Basic Research Program (No.2012CB720504; 2014CB744306), the Fundamental Research Fundsfor the Central Universities (No. 2013ZP0010), and GuangdongProvince NSF Team Project (No. S2011030001366).

References

[1] Y. Qu, The prospect of Chinas olen market during the twelfth ve-year plan,Petro. Petrochem. Today 20 (2012) 1625 (in Chinese).

[2] National Bureau of Statistics, China energy statistics yearbook, China Stat.Press, Beijing, 2010 (in Chinese).

[3] ICIS, China develops coal-to-olens projects, which could lead to ethylene self-sufciency, 2012 (assessed 25.08.2013), .

[4] P. Markewitz, W. Kuckshinrichs, W. Leitner, J. Linssen, P. Zapp, R. Bongartz, A.shown in Fig. 12. This means that the product cost of the MTOplant is highly affected by feedstock price and that for CTO plantsthe inuence is relatively small. Besides, coal price is more stablethan methanol which is mostly determined by oil price in the pastseveral years [18]. Although MTO plants have advantages of lowcapital investment and low environmental impact, their economicperformances are easily intervened by methanol price. In otherwords, MTO plants have less anti-risk capability of market uctu-ation than CTO plants in China. Expanding development of CTOplants with CCS should be encouraged since it could relieve theconict between the supply and demand of olens, meanwhile re-duce CO2 emissions, and manifest a strong anti-risk capability tothe raw material market.

5. Conclusions

Techno-economic performance of the CTO process with CCS wasanalyzed in this paper. The CTO process was also compared withthe MTO process. The performance results indicate that the CTOplant with CCS is slightly less thermodynamic efcient than theconventional CTO plant without CCS. For the CTO plant with 80%carbon capture compared to the CTO plant, the total capital invest-ment increases by 6%, from 2.52 104 RMB/t/y to 2.69 104 RMB/t/y, and the product cost rises nearly 11%, from 6442 RMB/t to7131 RMB/t.

The effects of economies of scale and carbon tax were also ana-lyzed. It was found that production scale has more effect on capitalinvestment than product cost. If the scale of the CTO plant with CCSincreases from 0.3 Mt/y to 2.0 Mt/y, the total capital investmentand product cost will drop approximately 53.2% and 19.3%. Themitigation cost of CTO with CCS is about 150 RMB/t, roughly equiv-alent to the current carbon price.

On the other hand, the product cost of the MTO plant is7896 RMB/t, which is much higher that of the CTO plant withCCS even in the context of carbon tax as high as 400 RMB/t.Although the MTO plant has low capital investment and CO2 emis-sions, its product cost ratio to the CTO plant with CCS is 0.9, itscumulative cash ow ratio is 0.7, and its economic performanceis susceptible to uctuation of market price. In contrast, the prod-uct cost of the CTOwith CCS is lower and it could resist market risk.In a word, developing CTO processes with CCS is important to thesustainable development of olens industry in China from theperspectives of resource reserve, economic performance, and envi-ronmental protection.

Acknowledgments

The authors are grateful for nancial support from the China

ng Journal 240 (2014) 4554 53Schreiber, T.E. Mller, Worldwide innovations in the development of carboncapture technologies and the utilization of CO2, Energy Environ. Sci. 5 (2012)72817305.

[5] K.Z. House, C.F. Harvey, M.J. Aziz, D.P. Schrag, The energy penalty of post-combustion CO2 capture & storage and its implications for retrotting the U.S.installed base, Energy Environ. Sci. 2 (2009) 193205.

[6] Z. Luo, M. Fang, M. Li, L. Gao, The Technology of CO2 Capture, Storage andUsage, China Elec. Power Press, Beijing, 2012 (in Chinese).

[7] H. Lin, H. Jin, L. Gao, W. Han, Techno-economic evaluation of coal-basedpolygeneration systems of synthetic fuel and power with CO2 recovery, EnergyConvers. Manage. 52 (2011) 274283.

[8] A. Pettinau, F. Ferrara, C. Amorino, Combustion vs. gasication for ademonstration CCS (carbon capture and storage) project in Italy: a techno-economic analysis, Energy 50 (2013) 160169.

[9] Q. Yi, B. Lu, J. Feng, Y. Wu, W. Li, Evaluation of newly designed polygenerationsystem with CO2 recycle, Energy Fuel 26 (2012) 14591469.

[10] K.S. Ng, Y. Lopez, G.M. Campbell, J. Sadhukhan, Heat integration and analysis ofdecarbonised IGCC sites, Chem. Eng. Res. Des. 88 (2010) 170188.

[11] H.C. Mantripragada, E.S. Rubin, Techno-economic evaluation of coal-to-liquids(CTL) plants with carbon capture and sequestration, Energy Policy 39 (2011)28082816.

[12] W. Zhou, B. Zhu, D. Chen, F. Zhao, W. Fei, Technoeconomic assessment ofChinas indirect coal liquefaction projects with different CO2 capturealternatives, Energy 36 (2011) 65596566.

[13] H. Han, Economic analysis of producing olen from naphtha, coal and naturalgas, Chem. Techno-Eco. 23 (2005) 1418 (in Chinese).

[14] X. Yang, L. Dong, Technical progress and economic analysis on the directproduction of light olens from syngas, Chem. Ind. Eng. Progr. 31 (2012) 17261731 (in Chinese).

[15] T. Ren, M.K. Patel, K. Blok, Steam cracking and methane to olens: energy use,CO2 emissions and production costs, Energy 33 (2008) 817833.

[16] T. Ren, M.K. Patel, Basic petrochemicals from natural gas, coal and biomass:energy use and CO2 emissions, Resour. Conserv. Recycl. 53 (2009) 513528.

[17] D. Xiang, L.J. Peng, S. Yang, Y. Qian, A review of oil and coal resource processesfor olens production, Chem. Ind. Eng. Progr. 32 (2013) 959970 (in Chinese).

[18] D. Xiang, Y. Qian, Y. Man, S. Yang, Techno-economic analysis of the coal-to-olens process in comparison with the oil-to-olens process, Appl. Energy 113

[24] K.S. Ng, J. Sadhukhan, Process integration and economic analysis of bio-oilplatform for the production of methanol and combined heat and power,Biomass Bioenergy 35 (2011) 11531169.

[25] Dalian institute of chemical physics, Chinese Academy of Sciences. The typicaloperating conditions and product component of methanol to olens, 2011(assessed 25.08.2013). . (inChinese).

[26] Y. Qian, J. Liu, Z. Huang, A. Kraslawski, J. Cui, Y. Huang, Conceptual design andsystem analysis of a poly-generation system for power and olen productionfrom natural gas, Appl. Energy 86 (2009) 20882095.

[27] Z. Li, D. Zhang, L. Ma, W. Logan, W. Ni, The necessity of and policy suggestionsfor implementing a limited number of large scale, fully integrated CCSdemonstrations in China, Energy Policy 39 (2011) 53475355.

[28] L. Zhou, S. Hu, D. Chen, Y. Li, B. Zhu, Y. Jin, Study on systems based on coal andnatural gas for producing dimethyl ether, Ind. Eng. Chem. Res. 48 (2009) 41014108.

[29] J. Cheng, C. Li, X. Cheng, The Review on Oil Replacement, China Petrochem.Press, Beijing, 2009 (in Chinese).

[30] R.T. Dahowski, C.L. Davidson, X.C. Li, N. Wei, A $70/t CO2 greenhouse gasmitigation backstop for Chinas industrial and electric power sects: insightsfrom a comprehensive CCS cost curve, Int. J. Greenh. Gas Con. 11 (2012) 7385.

[31] M.S. Peter, K.D. Timmerhaus, Plant Design and Economics for ChemicalEngineers, 5 ed., McGraw Hill, USA, New York, 2003.

[32] M. Orhan, I. Dincer, G. Naterer, Cost analysis of a thermochemical CuCl pilotplant for nuclear-based hydrogen production, Int. J. Hydrogen Energy 33(2008) 60066020.

[33] Y. Zhang, T.R. Brown, G. Hu, R.C. Brown, Techno-economic analysis of two bio-oil upgrading pathways, Chem. Eng. J. 225 (2013) 895904.

[34] K.S. Ng, N. Zhang, J. Sadhukhan, Techno-economic analysis of polygenerationsystems with carbon capture and storage and CO2 reuse, Chem. Eng. J. 219(2013) 96108.

[35] Chemical engineerings plant cost index, 2012 (assessed 25.08.2013), .

[36] J. Zhao, The Economic Data Express of China Petroleum and Chemical Industry,China Petro. Chem. Ind, Beijing, 2012 (in Chinese).

54 D. Xiang et al. / Chemical Engineering Journal 240 (2014) 4554(2014) 639647, http://dx.doi.org/10.1016/j.apenergy.2013.08.013.[19] L. Zhou, S. Hu, Y. Li, Q. Zhou, Study on co-feed and co-production system based

on coal and natural gas for producing DME and electricity, Chem. Eng. J. 136(2008) 3140.

[20] G. Liu, Z. Li, M. Wang, W. Ni, Energy savings by co-production: a methanol/electricity case study, Appl. Energy 87 (2010) 28542859.

[21] L.G. Zheng, E. Furinsky, Comparison of Shell, Texaco, BGL and KRW gasiers aspart of IGCC plant computer simulations, Energy Convers. Manage. 46 (2005)17671779.

[22] S. Yang, Q. Yang, H. Li, X. Jin, X. Li, Y. Qian, An integrated framework formodeling, synthesis, analysis, and optimization of coal gasication-basedenergy and chemical processes, Ind. Eng. Chem. Res. 51 (2012) 1576315777.

[23] K. Xie, D. Fang, Methanol Technology, Chem. Ind. Press, China, Beijing, 2010 (inChinese).[37] C.C. Cormos, Integrated assessment of IGCC power generation technology withcarbon capture and storage CCS, Energy 45 (2012) 434445.

[38] O. Lassagne, L. Gosselin, M. Desilets, M. Iliuta, Techno-economic study of CO2capture for aluminum primary production for different electrolytic cellventilation rates, Chem. Eng. J. 230 (2013) 338350.

[39] X. Hu, A. Li, H. Cheng, D. Xin, D. Zhang, B. Zheng, General Principles of theComprehensive Energy Consumption Calculation, China Stand. Press, Beijing,2008 (in Chinese).

[40] China Daily, China starts carbon trading in Shenzhen, 2013 (assessed25.08.2013), .

Techno-economic performance of the coal-to-olefins process with CCS1 Introduction2 Process modeling2.1 Coal-to-olefins process2.1.1 Coal gasification unit2.1.2 Methanol synthesis unit2.1.3 Methanol-to-olefins unit

2.2 Carbon capture and storage process

3 Analysis methodology4 Results and discussion4.1 Energy efficiency analysis4.2 Economic analysis4.2.1 Capital investment, product cost, and cumulative cash flow4.2.2 Effects of plant scale, carbon tax, and feedstock price

5 ConclusionsAcknowledgmentsReferences