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Applied Thermal Engineering 75 (2015) 371e383

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Applied Thermal Engineering

journal homepage: www.elsevier .com/locate/apthermeng

Black liquor gasification combined cycle with CO2 capture e Technicaland economic analysis

Elzimar Tadeu de Freitas Ferreira a, Jos�e Antonio Perrella Balestieri b, *

a Univ Estadual Paulista, Faculdade de Engenharia de Guaratinguet�a, Avenida Dr. Ariberto Pereira da Cunha, 333, Guaratinguet�a, SP, Brazilb Univ Estadual Paulista, Faculdade de Engenharia de Guaratinguet�a, Energy Department, Avenida Dr. Ariberto Pereira da Cunha, 333, 12516-410Guaratinguet�a, SP, Brazil

h i g h l i g h t s

� We analyzed configurations of BLGCC with and without CO2 capture and sequestration.� BLGCC was compared to the conventional pulp and paper backpressure/extraction steam cycle with Tomlinson boiler.� An exergetic analysis revealed values slightly lower or equal for the CO2 capture BLGCC scheme.� The economic attractiveness of BLGCC schemes was evaluated.

a r t i c l e i n f o

Article history:Received 25 May 2014Accepted 8 September 2014Available online 28 September 2014

Keywords:CogenerationBlack liquor gasificationCombined cycleExergetic analysisCO2 capture

* Corresponding author. Tel.: þ55 12 3123 2160.E-mail addresses: elzimartadeu@bol.com.br (E.T.F.

br, perrella@pq.cnpq.br (J.A.P. Balestieri).

http://dx.doi.org/10.1016/j.applthermaleng.2014.09.021359-4311/© 2014 Elsevier Ltd. All rights reserved.

a b s t r a c t

The pulp and paper sector is intensive in the use of energy, and presents a high participation in theindustrial context, specially based in the black liquor, a renewable source generated in the pulp process.Black liquor gasification is not still completely dominated; however, it has the potential of becoming animportant alternative for the pulp and paper sector. In this article, the traditional steam cycle based onchemical recovery and biomass boilers associated to backpressure/extraction turbine is compared toblack liquor gasification combined cycle schemes, associated to biomass boiler, considering the technicaland economic attractiveness of capturing and sequestering CO2. Results show that despite its interestingexergetic efficiency, the adoption CO2 capture system for BLGCC did not prove to be attractive under theprescribed conditions without major incentive.

© 2014 Elsevier Ltd. All rights reserved.

1. Introduction

In the pulp and paper sector, the importance of black liquor gasi-fication (BLG) to beburned in a combined cycle is assumed as away torecovering process chemicals with an improvement in the energyproduction of the plant. Traditionally, chemical recovery (Tomlinson)boiler associated to backpressure steam turbine is the availabletechnology for that, but an improvement in the thermal efficiency ofthis process and the availability of more electric energy can be ob-tained by the black liquor gasification combined cycle (BLGCC).

In a comparative analysis of conventional Tomlinson boiler withintegrated gasification combined cycle, Ref. [4] indicated the po-tential to double the power output if the conventional system isreplaced by this new technology. A hybrid combined cycle was also

Ferreira), perrella@feg.unesp.

6

proposed by N€asholm [4]; in which natural gas is burned in the gasturbine and the fuel gas obtained from black liquor gasificationwasused as a supplementary fuel for the steam cycle. Results of Ref. [4]indicated that no modifications were needed in the gas turbine forthis alternative solution, but the total efficiency was not as high asfor the integrated gasification combined cycle.

Ref. [33] presented a thermodynamic analysis of an integratedblack liquor gasification combined cycle cogeneration system. Anequilibrium model based on thermo-chemical data taken from astandard reference source was proposed and a commercial processsimulator was used for evaluate the combined cycle; an additionalpinch analysis was developed to identify potential heat sources tooptimize the proposed scheme.

In addition to the thermodynamic and equilibrium studies, it isalso important to detail the performance modeling of gasifiers andgas turbine cogeneration systems using different black liquor gas-ifiers modeled on proposed commercial designs; the paper byConsonni [40] identified prospective environmental, safety andinvestment cost benefits for the pulp industry.

E.T.F. Ferreira, J.A.P. Balestieri / Applied Thermal Engineering 75 (2015) 371e383372

Ref. [1] presented an analysis of black liquor pyrolysis andgasification expressing his expectancy that commercial biomassgasifier/gas turbine systems could be commercially available at theend of that decade, with a longer time for the commercialization ofgas turbine systems using black liquor gasification. A computerprogram for a thermodynamic comparison analysis of several blackliquor gasification combined cycle schemes was structured byGallego [2] to consider low and high gasification pressures, low andhigh temperatures and the use of air or oxygen. Air-blown andpressurized gasifiers were considered in that thermoeconomicanalysis and an exergetic analysis was presented to identify thelosses in the integrated gasification combined cycle.

Black liquor gasification combined cycle was also considered byHarvey [13]. A Swedish pulp mill state of the art commerciallyavailable technology was assumed as the basis for the calculationsand an off-design calculation was developed. Ref. [35] evaluated anair-blown biomass pressurized gasification integrated withadvanced combined cycle aiming at appraising the technical andeconomic feasibility of such technology for power production.

Ref. [30] reviewed several studies related to the black liquorgasification technologies and concluded that, despite they are stillunder development, they represent prospective environmental,safety, and investment costs benefits compared to the conventionalrecovery cycle and BLGCC has potential to switch pulp mills fromelectricity importers to electricity exporters, in the studied cases.Ref. [11] presented the results of experiments with oxygeninjected-gasifier with different oxygen mass ratios, concluding thatoxygen mass ratio decrease the formation of CO and H2 withincreasing oxygen mass ratio.

Ref. [6] demonstrated that the use of an integrated gasificationcombined cycle (IGCC) with CO2 capture and sequestration (CCS)technologies proves to be an important option for mitigatingemissions. Ref. [22]; in a previouswork, revealed thatwhen the costof carbon emissions is internalized, the cost of electricity producedcan become attractive, enabling the use of the proposed IGCC. Thecapture of CO2 froma plant that uses biomass represents a “negativeCO2 emission” thatopensup thepossibilityof trading carbon credits,increasing the financial attractiveness of the enterprise.

Ref. [24] developed an analysis of oxygen-blown pressurizedBLGCC for electricity production and a scheme with downstreamproduction of dimethyl ether (DME), both with and without CCS,compared to other recovery boiler-based pulping biorefinery con-cepts from economic and environmental points of view. One of themain conclusions was that if there is a possibility for imple-mentation of CCS, it significantly improves the economic perfor-mance in scenarios based on a high CO2 charge.

Fig. 1. Integrated pulp and paper mill with backp

In this paper, integrated gasification combined cycle schemeswere proposed based on the data of the business as usual (BAU)scheme in integrated pulp and paper mills, which is based on thechemical recovery boiler and backpressure/extraction steam tur-bine, associated to a biomass boiler for burning bark/wood residuesand wood chips. The alternative schemes are based on black liquorgasification combined cycle (BLGCC) associated to biomass boiler,considering the technical and economic attractiveness of capturingand sequestering CO2. An energetic and exergetic analysis for aBLGCC with and without CO2 capture system is presented; aneconomic analysis is also presented for comparing the BLGCCconfigurations with three fossil technologies in terms of technicaland economic parameters.

2. Proposal of a BLGCC scheme

Although the black liquor gasification is a process underdevelopment, the analysis of BLGCC schemes is of interest todetermine the most adequate operational conditions. According toRef. [27]; atmospheric low-temperature BLG is under demonstra-tion stage and pressurized high-temperature BLG under pilot state.Pettersson [24] explains that BLG development has gone from non-pressurized air-blown gasification to pressurized oxygen-blowngasification, with the advantage of smaller equipment and theability to produce the pulping process low- and medium-pressuresteam from gas cooling when pressurized process is chosen, add-ing that air-blown gasification can be used if electricity generationis envisaged.

In the present analysis, pressurized air-blown BLGCC schemes(with and without CO2 capture and sequestration) are proposedconsidering the availability of black liquor, bark and wood residues,as well as wood chips, of a conventional Brazilian pulp and paperintegrated mill, and they are compared to the conventional Tom-linson and biomass boiler steam cycle.

The steam distribution and the electric power for an integratedpulp and paper mill that produces 1200 ton/day of pulp and1000 ton/day of paper are presented in Fig. 1 [9]. In this case,220 ton/h (60.11 kg/s) of steam (at 60 bar) is produced by burning1740 ton/day (20.14 kg/s) of black liquor in the chemical recoveryboiler, and an additional 335 ton/h (90 kg/s) of steam is producedin the biomass boiler (it was assumed 530 kg/m3 as the density ofwood chips, according to Ref. [9]). High pressure steam isexpanded in a backpressure steam turbine and sent to the pro-cesses (at 12 bar and 4 bar). This scheme does not produce all theelectric power to supply the demand of 60 MW, and 22 MW is thenimported from the grid. An alternative consists in changing the

ressure/extraction cogeneration scheme [9].

Fig. 2. Integrated pulp and paper mill with extraction/condensing cogeneration scheme [9].

E.T.F. Ferreira, J.A.P. Balestieri / Applied Thermal Engineering 75 (2015) 371e383 373

steam turbine to a condensing/extraction (Fig. 2), in which thebiomass boiler needs to burn additional wood chips (augmentingfrom 720 m3/day to 2200 m3/day) to produce 270 ton/h of steam,totaling 490 ton/h, of which 155 ton/h are condensed and electricself-production is met.

Two pressurized air-blown black liquor integrated gasificationcombined cycle alternative solutions are then proposed, as follows:

� BLGCCeNCC (no CO2 capture) has the gasification unit, the gascleaning system, gas turbine unit, heat recovery steam generatorunit, steam turbine unit, condensing unit and the biomass boilerunit and corresponding fuel dryer system, with similarities withthe schemes of Refs. [4,7];

� BLGCCeCCS (CO2 capture/sequestration) has the same equip-ment and is based on similar data, but have a CO2 recovery unit.

In both cases, thermodynamic state of equipment is defined forthe present analysis according to the technological limits proposedby Refs. [7,21,36] relative to the gasification process. The proposal ofa CO2 separation unit, in this case, is identified by Refs. [3,10] as apre-combustion technology, in which the carbon dioxide isremoved of the exhaust gases before the combustion.

Fig. 3. Simplified air-blown

Fig. 3 illustrates a simplified BLGCC scheme proposed to be in-tegrated to a pulp and paper mill with CO2 capture, whose numbersare related to the number of flow of Figs. 4 and 5, obtained from theCycle Tempo software V, whose main units are identified by grayboxes. In the same figure, BLGCCeNCC can be identified justexcluding the equipment contained by the dotted line. Thermo-dynamic data is available in Table 1 for BLGCCeNCC. Data relative toBLGCCeCCS is presented in Table 2 just for the thermodynamicpoints that differs from Table 1. In these figures and tables, the valueof enthalpy relative to fuel and exhaust gas present negativevalues e according to Ref. [44]; this is explained by the conventionassumed by the Cycle Tempo software, in which an energy flowfrom the system to the environment must have a positive sign, andvice-versa. Technical and economic data of biomass boiler do notvary for both configurations.

The pressurized air-blown gasifier option is considered in themodeling due to its low cost in comparison to the other gasificationprocesses. The input values of black liquor for the gasifier and ofbark/wood residues andwood chips for the biomass boiler are takenfrom the backpressure/extraction cogeneration scheme of Fig. 1,which represents the typical value of a Brazilian pulp and papermill.The same is applied to the biomass boiler for both configurations.

BLGCCeCCS scheme.

Fig.

4.Air-blownBL

GCC

eNCC

.

E.T.F. Ferreira, J.A.P. Balestieri / Applied Thermal Engineering 75 (2015) 371e383374

Fig.

5.Air-blownBL

GCC

eCC

S.

E.T.F. Ferreira, J.A.P. Balestieri / Applied Thermal Engineering 75 (2015) 371e383 375

Table 1Thermodynamic data of BLGCCeNCC.

Flow Medium Mass flow [kg/s] Pressure [bar] Temperature [�C] Enthalpy [kJ/kg] Entropy [kJ/kg K] Exergy [kJ/kg] Quality [%]

1 Water/steam 2.81 4.00 165.72 2787.76 7.0116 768.95 100.002 Fuel 20.14 25.00 115.00 �7600.52 2.1038 15,528.983 Fuel 20.05 25.00 115.00 �7548.38 2.1046 15,528.714 Gas 54.54 25.00 950.00 �1837.00 8.6688 5614.255 Gas 49.54 25.00 950.35 �1336.14 8.2241 5069.786 Gas 54.63 25.00 948.85 �1833.35 8.6571 5661.347 Gas 4.99 25.00 950.35 �6801.05 12.2740 11,254.498 Water/steam 26.53 12.00 275.53 2933.27 6.9389 995.43 100.009 Gas 0.09 25.00 115.00 75.71 0.6935 34,147.6710 Gas 54.54 23.50 948.85 �1838.67 8.6879 5607.0511 Gas 0.09 25.00 948.85 �1392.56 2.4046 34,971.4612 Gas 54.54 23.50 500.00 �2463.18 8.0530 5165.5013 Gas 1.50 23.50 500.00 �147.97 6.2592 15,525.1014 Gas 53.04 23.10 500.00 �2528.44 8.0761 4881.3715 Water/steam 73.02 6.00 120.28 505.25 1.5305 65.85 0.0016 Water/steam 22.49 4.00 165.72 2787.76 7.0116 768.95 100.0017 Water/steam 26.53 12.00 275.79 2993.26 6.9388 995.43 100.0018 Water/steam 73.02 4.00 158.69 2722.29 6.9761 763.72 100.0019 Water/steam 2.81 4.00 165.72 2787.76 7.0116 768.95 100.0020 Gas 205.50 1.01 15.00 �98.85 6.8652 0.1521 Gas 205.50 22.20 497.59 405.71 6.9973 466.6522 Gas 189.06 22.20 497.59 405.71 6.9973 466.6523 Gas 224.06 1.040 610.20 �1221.70 8.0471 350.0624 Water/steam 26.53 12.00 275.73 2993.27 6.9389 995.43 100.0025 Water/steam 73.02 2.00 120.21 504.68 1.5301 65.38 0.0026 Gas 224.06 1.040 143.00 �1742.26 7.2146 69.3927 Gas 16.44 22.20 497.59 405.71 6.9973 466.6528 Water/steam 25.30 4.00 165.72 2787.76 7.0116 768.95 100.0029 Gas 34.49 27.30 445.19 348.50 6.8608 448.7630 Water/steam 1759.53 1.00 30.00 125.83 0.4368 1.58 0.0031 Water/steam 4413.15 1.00 39.01 163.49 0.5592 3.96 0.0032 Water/steam 0.00 1.00 15.00 63.08 0.2245 0.00 0.0033 Water/steam 0.00 1.00 15.00 63.08 0.2245 0.00 0.0034 Gas 34.49 27.30 393.19 292.40 67.798 416.0235 Gas 207.62 21.70 1418.00 �341.49 8.0009 1387.1636 Water 1759.53 1.00 39.01 163.49 0.5592 3.96 0.0037 Gas 224.06 21.70 1357.23 �286.66 7.9512 1312.7138 Gas 154.57 22.20 497.59 405.71 6.9973 466.6539 Gas 224.06 1.040 462.78 �1392.62 7.8355 240.1040 Gas 224.06 1.040 328.00 �1543.47 7.6092 154.4541 Water/steam 102.36 4.010 135.00 567.82 1.6871 83.28 0.0042 Water/steam 51.83 95.00 136.63 580.83 1.6951 94.00 0.0043 Water/steam 2.81 4.00 165.72 2787.76 7.0116 768.95 100.0044 Water/steam 73.02 2.00 151.55 2772.29 7.2885 673.72 100.0045 Water/steam 1759.53 2.00 30.01 125.97 0.4369 1.68 0.0046 Water/steam 26.53 2.00 260.94 2993.26 7.7516 761.23 100.0047 Water/steam 26.53 2.00 120.21 504.68 1.5301 65.38 0.0048 Water/steam 26.53 6.00 120.28 505.25 1.5305 65.85 0.0049 Water/steam 4413.15 1.00 30.00 125.83 0.4368 1.58 0.0050 Water/steam 4413.15 2.00 30.01 125.97 0.4369 1.68 0.0051 Water/steam 99.55 4.01 120.31 505.25 1.5310 65.69 0.0052 Water/steam 98.24 95.00 307.25 1443.83 3.4236 458.91 4.2953 Water/steam 73.02 4.00 158.69 2772.29 6.9761 763.72 100.0054 Gas 34.89 22.20 497.59 405.71 6.9973 466.6555 Gas 34.89 22.20 397.59 297.13 6.8464 401.5456 Water/steam 98.24 95.00 307.25 1386.02 3.3240 429.80 0.0057 Water/steam 98.24 95.00 307.25 1405.71 3.3579 439.72 1.7058 Water/steam 102.36 95.00 136.63 580.83 1.6951 94.00 0.0059 Water/steam 51.83 95.00 136.63 580.83 1.6951 94.00 0.0060 Water/steam 50.33 95.00 136.63 580.83 1.6951 94.00 0.0061 Water/steam 51.83 95.00 295.00 1315.54 3.2013 394.69 0.0062 Water/steam 181.79 95.00 307.25 1386.02 3.3240 429.80 0.0063 Water/steam 83.56 95.00 307.25 1386.02 3.3240 429.80 0.0064 Water/steam 83.56 95.00 307.25 1790.53 4.0210 633.49 30.0065 Water/steam 353.81 95.00 307.25 1386.02 3.3240 429.80 0.0066 Water/steam 98.24 95.00 307.25 1790.53 4.0210 633.49 30.0067 Water/steam 51.83 95.00 307.24 2734.38 5.6471 1108.79 100.0068 Water/steam 51.83 90.00 534.36 3473.27 6.7689 1524.42 100.0069 Water/steam 98.24 95.00 307.25 1386.02 3.3240 429.80 0.0070 Water/steam 51.83 95.00 197.83 846.07 2.2980 185.49 0.0071 Water/steam 353.81 95.00 307.25 1655.69 3.7886 565.59 20.0072 Water/steam 50.53 95.00 307.24 2734.38 5.6471 1108.79 100.0073 Gas 62.87 1.00 404.89 �3005.41 7.8047 625.3774 Gas 52.35 1.01 15.00 �98.85 6.8653 0.12

E.T.F. Ferreira, J.A.P. Balestieri / Applied Thermal Engineering 75 (2015) 371e383376

Table 1 (continued )

Flow Medium Mass flow [kg/s] Pressure [bar] Temperature [�C] Enthalpy [kJ/kg] Entropy [kJ/kg K] Exergy [kJ/kg] Quality [%]

75 Gas 52.35 1.04 18.21 �95.61 6.8681 2.5776 Gas 52.35 1.01 349.77 246.07 7.6570 116.9077 Fuel 10.60 1.01 15.00 �4065.65 1.6653 20,167.0778 Gas 62.87 1.00 569.09 �2808.36 8.0633 747.9079 Water/steam 50.33 90.00 518.96 3434.95 6.7210 1499.90 100.0080 Gas 62.87 1.00 176.21 �3265.22 7.3384 499.9481 Gas 62.87 1.01 2273.82 �460.57 9.5621 2663.8282 Water/steam 50.33 4.00 155.60 2765.40 6.9601 761.44 100.0083 Gas 62.87 1.01 1008.12 �2245.35 8.5984 1156.7284 Water/steam 50.33 95.00 136.63 580.83 1.6951 94.00 0.0085 Gas 62.87 1.01 177.75 �3263.53 7.3393 501.3586 Gas 0.077 1.01 1147.00 �4046.27 5.1996 1003.7287 Fuel 10.60 1.01 70.00 �4023.76 1.9278 20,133.3488 Gas 4.00 0.100 15.00 �15,908.52 3.7364 �0.0989 Gas 224.06 1.04 99.17 �1788.09 7.0982 57.0990 Gas 34.49 27.30 393.19 292.40 6.7798 416.0291 Gas 0.00 27.30 393.19 292.40 67.798 416.0292 Gas 228.06 1.01 98.26 �1990.73 7.1905 57.5193 Gas 4.00 0.10 70.00 �13,341.24 11.810 243.3794 Gas 228.06 1.01 93.41 �1992.68 7.1853 57.08

E.T.F. Ferreira, J.A.P. Balestieri / Applied Thermal Engineering 75 (2015) 371e383 377

The technical analysis of BLGCCeNCC revealed that its netthermal efficiency is of 34.13% for a gross electric power generatedof 162.6 MW (with 100.6 MW in the gas turbine and 62 MW in thesteam turbine) and an energy content of black liquor and residuesof 464 MW. As total demand of pulp and paper mill is of 60 MW, asurplus of 100.6 MW is available to be commercialized to the grid,which improves the economic attractiveness of this investment. Bythe other side, BLGCCeCCS presents a net thermal efficiency of27.57% and a gross electric power generated of 134.1 MW, with81.6 MW in the gas turbine and 52.5 MW in the steam turbine, witha surplus of 74.1 MW. The reduction of 6.56% in the net thermalefficiency is due to the augmented auxiliary power consumption ofCO2 capture equipment.

3. Modeling and exergetic analysis of BLGCC

Thermodynamic analysis is applied in the modeling of cogene-ration schemes according to the equations relative to mass con-servation, as expressed by Eq. (1) assuming that steady state for theanalysis, and by the first and second laws of Thermodynamics,defined by Eqs. (2) and (3) for steady state. Subscripts “i”, “e” and “j”refer respectively to the inlet, exit and heat flows over the controlvolume (CV) for heat flow ð _QÞ, axis power ð _WÞ and generated en-tropy ð _SÞ in terms of mass flow ð _mÞ, specific enthalpy (h) and spe-cific entropy (s).X

_me ¼X

_mi (1)

_Qcv ¼X

_mehe �X

_mihi þ _Wcv (2)

_Sgercv þXj

_Qcvj

Tj

!þX

_misi �X

_mese ¼ 0 (3)

In the exergetic analysis, exergy is presented in its separatedcomponents (Eq. (4)). Kinetic and potential exergy will not beconsidered in the present analysis; physical and chemical specificexergy are expressed, respectively, by Eqs. (5) and (6). Referencestate was defined as P0 ¼ 101 kPa and T0 ¼ 298 K (h0 ¼ 104.9 kJ/kg,s0 ¼ 0.3672 kJ/kg K).

_Ex ¼ _Exc þ _Exp þ _Exf þ _Exq (4)

exf ¼_Exf_m

¼ h� h0 � T0ðs� s0Þ (5)

exq ¼_Exq_m

¼Xj

xjejQ þ RT0Xj

xj ln xj (6)

Exergy analysis is developed considering the irreversibility(destroyed exergy) and exergetic efficiency, as defined respectivelyby Eqs. (7) and (8). For Eq. (8), the sum of exit exergy represents theproducts and the sum of inlet exergy represents the “fuel” of eachcomponent under analysis.

_Ed ¼Xj

1� T0

Tj

!_Qj � _Wvc þ

Xi

_m$exi �Xe

_m$exe (7)

hII ¼P _ExeP _Exi

(8)

3.1. Gasifier modeling

For the analysis of the synthesis gas production by the gasifi-cation of black liquor, a chemical composition for this residue isdefined, consistent with some of the ones presented in Ref. [29].The black liquor ultimate analysis presented in Table 3 was adaptedfrom Ref. [28]. A previous multi-effect evaporation process isapplied for concentration of the black liquor.

The expression by Ref. [38] in Eq. (9) is considered for estimatingthe black liquor higher heating value (HHV) for the compositionpresented in Table 3. Ref. [41] considers that liquors with highcalorific value tend to have high percentage of carbon and lowlevels of oxygen and sodium. The higher heating value of 14.35 MJ/kg is obtained for the considered black liquor composition. Thisrepresents a value higher than the 12.00 MJ/kg average black liquorheating value for Brazilian conditions [32]. Typical higher heatingvalue of black liquor is in the range of 13.40e15.50 MJ/kg [16,29].

HHV ¼ 0:3491 Cþ 1:1783 Hþ 0:1005 S� 0:1034 O� 0:0151 N

� 0:0211 A

(9)

Table 2Thermodynamic data of BLGCC-CCS (just flows with distinct values).

Flow Medium Mass flow [kg/s] Pressure [bar] Temperature [�C] Enthalpy [kJ/kg] Entropy [kJ/kg K] Exergy [kJ/kg] Quality [%]

8 Water/steam 27.37 12.00 277.06 2996.21 6.9442 996.83 100.0015 Water/steam 58.13 6.00 120.28 505.25 1.5305 65.85 0.0016 Water/steam 14.73 4.00 166.81 2790.16 7.0171 769.78 100.0017 Water/steam 27.37 12.00 277.06 2996.21 6.9442 996.83 100.0018 Water/steam 58.13 4.00 159.59 2774.27 6.9807 764.38 100.0019 Water/steam 2.41 4.00 166.81 2790.16 7.0171 769.78 100.0023 Gas 218.75 1.040 556.75 �1147.13 7.9766 303.1724 Water/steam 27.37 12.00 277.06 2996.21 6.9442 996.83 100.0025 Water/steam 58.13 2.00 120.21 504.68 1.5301 65.38 0.0026 Gas 218.75 1.04 150.00 �1596.29 7.2370 67.1227 Gas 16.44 22.20 497.59 405.71 6.9973 466.6528 Water/steam 17.14 4.00 166.81 2790.16 7.0171 769.78 100.0030 Water/steam 1817.53 1.00 30.00 125.83 0.4368 1.58 0.0031 Water/steam 3516.13 1.00 39.01 163.49 0.5592 3.96 0.0035 Gas 202.31 20.80 1316.15 �334.69 7.9298 1264.9236 Water/steam 1817.53 1.00 39.01 163.49 0.5592 3.96 0.0037 Gas 218.75 20.80 1260.36 �279.05 7.8819 1198.5439 Gas 218.75 1.04 424.43 �1298.32 7.7793 209.1340 Gas 218.75 1.04 328.00 �1405.37 7.6132 149.6641 Water/steam 88.91 4.01 135.00 567.82 1.6871 83.28 0.0042 Water/steam 44.51 95.00 136.63 580.83 1.6951 94.00 0.0043 Water/steam 2.41 4.000 166.81 2790.16 7.0171 769.78 100.0044 Water/steam 58.13 2.000 152.51 2774.27 7.2931 674.36 100.0045 Water/steam 1817.53 2.000 30.01 125.97 0.4369 1.68 0.0046 Water/steam 27.31 2.000 262.40 2996.20 7.7571 762.59 100.0047 Water/steam 27.31 2.000 120.21 504.68 1.5301 65.38 0.0048 Water/steam 27.31 6.000 120.28 505.25 1.5305 65.85 0.0049 Water/steam 3516.13 1.000 30.00 125.83 0.4368 1.58 0.0050 Water/steam 3516.13 2.000 30.01 125.97 0.4369 1.68 0.0051 Water/steam 85.50 4.010 120.31 505.25 1.5310 65.69 0.0053 Water/steam 58.13 4.000 159.59 2774.27 6.9807 764.38 100.0058 Water/steam 87.91 95.00 136.63 580.83 1.6951 94.00 0.0059 Water/steam 44.51 95.00 136.63 580.83 1.6951 94.00 0.0060 Water/steam 43.40 95.00 136.63 580.83 1.6951 94.00 0.0061 Water/steam 44.51 95.00 295.00 1315.54 3.2013 394.69 0.0062 Water/steam 156.13 95.00 307.25 1386.02 3.3240 429.80 0.0063 Water/steam 57.89 95.00 307.25 1386.02 3.3240 429.80 0.0064 Water/steam 57.89 95.00 307.25 1790.53 4.0210 633.49 30.0065 Water/steam 303.862 95.00 307.25 1386.02 3.3240 429.80 0.0067 Water/steam 44.51 95.00 307.24 2734.38 5.6471 1108.79 100.0068 Water/steam 44.51 90.00 536.04 3477.43 6.7740 1527.09 100.0070 Water/steam 43.40 95.00 197.83 846.07 2.2980 185.49 0.0071 Water/steam 303.86 95.00 307.25 1655.69 3.7886 565.59 20.0072 Water/steam 43.40 95.00 307.24 2734.38 5.6471 1108.79 100.0079 Water/steam 43.40 90.00 521.33 3440.86 6.7284 1503.66 100.0082 Water/steam 43.40 4.00 157.16 2768.87 6.9682 762.58 100.0083 Gas 62.87 1.01 951.39 �2318.26 8.5399 1100.6784 Water/steam 43.40 95.00 136.63 580.83 1.6951 94.00 0.0086 Gas 0.08 1.01 1347.00 �3845.27 5.3320 1166.5788 Gas 4.00 0.10 15.00 �15908.52 3.7364 �0.0989 Gas 218.75 1.04 105.08 �1643.23 7.1198 53.9792 Gas 222.75 1.01 103.95 �1853.30 7.2142 54.3793 Gas 4.00 0.10 70.00 �13,341.24 11.8010 243.3794 Gas 222.75 1.01 90.00 �1868.00 7.1745 51.1295 Gas 53.04 23.10 490.00 �2541.75 8.0588 4873.0696 Gas 53.04 22.46 553.40 �2541.75 8.0820 4866.3697 Gas 53.04 22.46 543.40 �2555.46 8.0653 4857.4698 Gas 53.04 21.84 552.45 �2555.46 8.0697 4856.2099 Gas 53.04 21.84 542.45 �2569.20 8.0530 4847.29100 Gas 53.04 23.84 544.26 �2566.72 8.0268 4857.31101 Gas 53.04 22.84 553.59 �2553.89 8.0597 4861.52102 Gas 53.04 22.84 543.59 �2567.64 8.0399 4852.60103 Gas 53.04 23.84 544.26 �2552.97 8.0435 4866.24104 Gas 47.74 21.84 544.26 �2566.72 8.0560 4848.89105 Gas 0.00 21.84 544.26 �2566.72 8.0560 4848.89106 Gas 5.30 21.84 544.26 �2566.72 8.0560 4848.89107 Gas 5.30 20.00 104.26 �3140.88 7.0836 4554.91108 Gas 5.30 17.23 37.78 �3222.42 6.8959 4527.48110 Gas 47.74 21.30 414.26 �2742.65 7.8300 4738.07111 Gas 0.00 21.30 544.26 �2566.72 8.0643 4846.48

E.T.F. Ferreira, J.A.P. Balestieri / Applied Thermal Engineering 75 (2015) 371e383378

Table 3Chemical composition of black liquor organic fraction, dry basis.

Composition Percentage (mass)

C 36.51H 4.00O 35.60N 0.0S 5.6

Source: [28].

Table 5Molar composition of the gas that leaves the combustion chamber.

Compositionof the gas

Gas leaving combustionchamber

Gas leaving gas turbine

xi (V%) xi (V%)

CO2 9.72 8.98H2O 6.79 6.35N2 72.26 72.65O2 10.37 11.16Ar 0.86 0.86Sum 100.00 100.00

E.T.F. Ferreira, J.A.P. Balestieri / Applied Thermal Engineering 75 (2015) 371e383 379

For the calculation of black liquor exergy, empirical correlationsfor solid dry fuels given by Eq. (10) and by Eq. (11) are considered[12,42], being e0 the fuel specific exergy. Equation (11), which ac-curacy is of ±2%, is valid for (O/C) < 0.5, in which H, C, O and N arethe mass fractions presented in Table 3, for which b ¼ 1.1394 isobtained.

b ¼ e0

LHV(10)

b ¼ 1:0437þ 0:0140HCþ 0:0968

OCþ 0:0467

NC

(11)

The lower heating value of black liquor (LHV) is obtained fromEq. (12) [20] taking the value of the HHV of 14.35 MJ/kg previouslycalculated and 4% of hydrogen content, according to Table 3,resulting 15.35 MJ/kg for the specific exergy of black liquor.

LHV ¼ HHV� 2442ð9:01HÞ (12)

According to Ref. [17]; the reactor temperature is in the range900 �Ce1100 �C. The analysis of power generation of BLGCC cycle isbased on the composition of the syngas operating with pressurizedair at 25 bar and 950 �C. The molar fractions of the synthesis gascomposition exiting the gasifier are presented in Table 4. Simulatedresults were obtained by the kinetic modeling of Cycle-Tempocommercial software [43].

Ref. [45] considers that the high heating value of product gas(HHVg) can be calculated with Eq. (13), in which the value isexpressed in MJ/Nm3. The higher heating value of 5.251 MJ/Nm3 isobtained for the considered gas composition of simulation, inwhich yH2

; yCO; yCH4and yH2S are the mole fractions of H2, CO, CH4

and H2S, respectively.

HHVg ¼ 12:75yH2þ 12:63yCO þ 39:82yCH4

þ 25:105yH2S (13)

3.2. Combined cycle modeling

The thermodynamic analysis for the gas turbine considered thatcompressor present air extractions for intermediate cooling ofstages and part of the air is sent to the gasification process. Theexhaust gas composition data leaving the combustion chamber ispresented in Table 5.

Table 4Molar fractions of compositions and operational conditions of gasifier.

Composition Molar fraction (mol)

CH4 0.0017CO 0.2661CO2 0.0805H2O 0.0694H2 0.1429N2 0.4342H2S 0.0000Ar 0.0052Temperature (�C) 950Pressure (bar) 25

Due to the change of original fuel by a low heating value fuel asthe synthesis gas, modifications in the compressor structure andcombustion chamber are expected [23]. In this case, as described byKlimantos [35]; the use of one or more control strategies must beadopted in order to avoid compressor instability problems.Bleeding air from the compressor is one of these control strategiesand a ratio (l) of 1.7e2.0 for fuel gas to air bleed flow is consideredin the same reference; for the proposed scheme, the fuel tobleeding air ratio was estimated as 1.86 according to the thermo-dynamic data of syngas. Assuming full load and a mechanical effi-ciency (hm) of 0.99, according to Ref. [7]; to take into accounttransmission box and electric generator, a net power of 100,616 kWwas obtained for the gas turbine.

Based on the synthesis gas composition, the molar compositionof the exhaust gas that leaves the gas turbine is presented inTable 5. This gas is send to the heat recovery steam generator beforebeing sent to the stack. Table 6 presents the exergetic efficiencycalculated according to Eq. (8) for the main components ofBLGCCeNCC and BLGCCeCCS, as well as the net exergetic efficiencyconsidering inputs and outputs of configurations.

4. Economic evaluation of BLGCC configurations

For assessing the financial attractiveness of a power generationproject, indicators that take into account the investment cost of theproject, the electricity production, the annual income, expensesand deductions are necessary. With such indicators, a demonstra-tion of results comprising the annual project revenue, annual in-vestment inflows and outflows, fixed and variable operating costs,depreciation of equipment, and tax deductions for the constructionof the cash flow to over the life of the project is structured. A cashflow is then provided for the investors to subsidize the economicand financial analysis and to determine the attractiveness of theinvestment.

The main indicators commonly used in the economic evaluationof projects, which will be developed in the present modeling,consist of Net Present Value (NPV), Internal Rate of Return (IRR),Investment Recovery (Payback) and the Cost of Electricity (COE), asshortly described in the sequence. In the Net Present Value, therevenues and costs of a project are estimated and discounted (for

Table 6Exergetic efficiency for the main components of BLGCC configurations.

Description of components BLGCCeNCC BLGCCeCCS

hII (%) hII (%)

Gasifier 85.70 86.32Gas turbine 75.36 63.33Heat recovery steam generator 86.07 84.79Steam turbine 89.80 89.80Biomass boiler 38.98 33.62Net plant exergetic efficiency 30.07 24.30

E.T.F. Ferreira, J.A.P. Balestieri / Applied Thermal Engineering 75 (2015) 371e383380

an assumed project lifetime, k, and interest rate, i) to a reference(initial) date and compared to the initial investment. Projects withnegative NPV should be rejected and the preferred project is thehighest positive NPV.

The Internal Rate of Return (IRR) is defined as the discount ratefor which a zero NPV of the project cash flow can be obtained.Payback measures the length of time required to recover an initialinvestment ignoring the cash flows that occur after such period. It isnot recommended the use of payback solely and exclusively as aneconomic indicator; however, it can be presented in conjunctionwith another economic method.

The average cost of electricity (COE) is the ratio defined by thesummation of annualized cost of investment, the cost of operationand the maintenance and the fuel cost of a project relatively to theannual electricity generation of the project [34], as presented by Eq.(14). For the purpose of the present modeling, it is considered theinvestment cost of equipments, the selling price of electricity ac-cording to the Brazilian electric sector, the cost of biomass in thepulp and paper sector, the fuel consumption and power surpluselectricity by the considered configurations. The generation of cashflows for this analysis is based on the Brazilian Income Tax Law [25],social contribution on the net income (Law N� 7,689/1988) and thestraight-line depreciation [26].

COE¼ðannuity factor � investmentsÞþO&Mþ fuel costdeliveredenergy

�$

kWh

�(14)

Table 7 presents the main data of BLGCC project taken as areference (BLGCCeNCC) and for the scheme with CO2 capture(BLGCCeCCS). The initial investment was based on Ref. [8] andadjusted according to Ref. [39]. Fuel cost for black liquor wasadopted from Ref. [5]. The assumption of 8330 h/year of operationalhours and an interest rate of 12% per year are proposed by Larson[8]; values considered as more adequate for the analysis of a realcondition. A credit carbon of 6 US$/ton of CO2 captured wasconsidered for BLGCCeCCS [31]. Payback of 4.2 and 5.6 years areconsidered high for private investors, however, it must be takeninto account that black liquor is an environmental problem thatmust be solved without disposing it due to the need of recoveringcaustic products.

An economic comparison of CO2 separation and capture tech-nologies was performed in Ref. [19] for three types of power plants- integrated coal gasification combined cycle, IGCC; pulverized coal,PC; and natural gas combined cycle, NGCC. In PC and NGCC plants,the CO2 capture method was based on monoethanolamine (MEA)scrubbing of flue gas, and for IGCC power plant a physical

Table 7BLGCC economic data.

Parameters BLGCCeNCC BLGCCeCCS

Black liquor cost ($/MWh) 0.0005Annual capacity factor (%) 95.09Operation hours (h/year) 8330Economic life (years) 25Interest rate (% per year) 12Production of electricity (MWh) 1,318,631 1,065,310Exported electricity (MWh) 838,131 679,672Initial investment (106 US$) 210.9 233.43Investment cost (US$/kW) 1332 1825Cost of electricity (US$/MWh) 23.59 32.38Annual revenue (106 US$) 77.40 65.53Earning (106 US$) 42.73 33.96Internal Rate of Return e IRR (%) 24.15 18.27Net Present Value e NPV (106 US$) 190.40 106.19Payback (years) 4.1 5.4

absorption process to capture CO2 from the high pressure synthesisgas was proposed; in all the cases, 90% capture efficiency wasspecified.

BLGCCeNCC and BLGCCeCCS are compared to above thermo-electric plants based on Refs. [14,15,18,19] data. For each technol-ogy, a thermoelectric plant without CO2 capture is taken as areference (baseline) and the same technology with CO2 capture isthen evaluated. In the present study, costs due to CO2 trans-portation and storage are not considered.

The values of investment cost (C), net power output, CO2emitted, thermal efficiency (based on LHV) and heat rate, HR (basedon LHV), were calculated for BLGCCeNCC and BLGCCeCCS; for coalIGCC, pulverized coal and natural gas combined cycle, values pro-jected for the year 2012 by Herzog [14] are considered in thisanalysis. The cost of electricity (COE) due to investment, fuel costand operation and maintenance is calculated for reference andcapture plant, in mills/kWh, respectively, by Eqs. (15)e(17). Thetotal cost of electricity, in ¢/kWh, is given by equation (18). Thefollowing values were considered: interest rate (r) of 15% a year;annual capacity factor (f) of 0.75 (equivalent to 6570 h/year); fuelcost (FC) for natural gas of 2.93 $/MMBTU based on LHV; and fuelcost (FC) for coal of 1.24 $/MMBTU based on LHV. O&M cost isassumed to be broken down into a fixed and variable cost in theproportion 65%e35%; as in Ref. [18] several annual capacity factorwas considered in the analysis, the value of 6570 h/year is taken asoriginal value (forig), assumed as the adjusted common economicbasis.

COEinvestment ¼1000:r:c

f(15)

COEfuel ¼HR:FC1000

(16)

COEO&M ¼ 0:35ðCOEO&MÞorig$forigf

þ 0:65ðCOEO&MÞorig (17)

COE ¼ COEinvestment þ COEfuel þ COEO&M

10(18)

For the economic/environmental comparison of technologies(Table 8), the following parameters are calculated for the referenceand capture plants of each considered technologies, according toEqs. (19) and (21): incremental cost of electricity (DCOE, in ¢/kWh);energy penalty (EP, in %) which measures the reduction in netpower output ( _Wnet, in kW) of the capture plant compared to thereference plant for equal fuel inputs; cost of CO2 mitigation (MC, in$/ton of CO2 avoided). Ref. [37] defines specific CO2 emission (SE, inkg/kWh) for reference a plant that is calculated considering the CO2emission factor (EF, in kg/TJ) of each fuel, the fuel mass flow ( _mfuel,in kg/s) and lower heating value (LHV, in kJ/kg) and the net poweroutput of each plant (Eq. (22)).

DCOE ¼ COEcapture � COEref (19)

EP ¼_Wnet;ref � _Wnet;capture

_Wnet;capture(20)

MC ¼ COEcapture � COErefSEref � SEcapture

*10 (21)

SE ¼ EFCO2$ _mfuel$LHV

106$ _Wnet(22)

Table 8Performance of BLGCC compared to Ref. [14] data for IGCC, PC and NGCC.

The gray shaded and blue colored values signify the results of our simulation (theother three columns are data taken from Ref. [14]).

E.T.F. Ferreira, J.A.P. Balestieri / Applied Thermal Engineering 75 (2015) 371e383 381

For the simulation of BLGCC installation, data presented in thisstudy will be classified as “not adjusted” relatively to the Brazilianreference interest rate of 12% a year and 8330 h/year, and“adjusted” considering interest rate of 15% a year and 6570 h/year;fuel cost for black liquor of 0.00003695 $/MMBTU based on LHVwas the same for both conditions (Table 8).

For a sensibility analysis relative to the variability of interestrate and the electricity price sold to the grid, three scenarios werecomposed. The optimistic scenario is addressed to a favorableeconomic condition for Brazil in terms of interest rate (8% peryear) and an augmentation of revenues due to better sellingelectricity price (0.10 US$/kWh), base scenario is the actualcondition (12% per year and 0.08 US$/kWh) and pessimisticscenario expresses the worst condition (16% per year and0.06 US$/kWh).

Figs. 6e8 illustrate, respectively, net present value, internal rateof return and the cost of electricity for the base, optimistic andpessimistic scenarios of BLGCCeNCC and BLGCCeCCS varying the

Fig. 6. Net present value of BLGCC configurations f

percentage of capital borrowing from 70% to 130%, considering thatsome percent of the capital for the plant has to be covered byforeign currency. It can be verified that net present value and in-ternal rate of return decrease and cost of electricity grows the morethe capital borrowing percentage; NPV becomes negative for 80% ofcapital borrowing when pessimistic 16% interest rate is consideredfor BLGCCeCCS and 110% for the same scenario when BLGCCeNCCis considered. In Fig. 7, the worst scenario for BLGCCeNCC is coin-cident with the base scenario for BLGCCeCCS.

The cost of electricity was also varied against the operationalhours from 6500 to 8760 h/year, revealing that even for the worstscenario of BLGCCeNCC and BLGCCeCCS considering 130% of cap-ital borrowing, the cost of energy is ever less than the electric en-ergy selling price of pessimistic scenario, of 0.06 US$/kWh. The costof energy is also varied against the operational hours (Fig. 9) forstating the adequateness of higher operation periods.

5. Conclusions

Two air-blown black liquor integrated gasification combinedcycle configurations (with and without CO2 capture system)were modeled and an exergetic analysis developed for assessingtheir potentialities. An economic analysis was also developed,and the BLGCC configurations were compared to fossil fueltechnologies.

The energetic results of the proposed BLGCC cycle werecompared to the conventional steam cycle based on the Tomlinsonboiler. For the supplying of steam to the processes of an integratedpulp and paper mill that produces 1200 ton/day of pulp and1000 ton/day of paper and demands 60 MW of electric power,BLGCCeNCC configuration presented a thermal efficiency of 34%and a surplus of 100.6 MW against thermal efficiency of 28% and asurplus of 74.1 MW for the BLGCCeCCS configuration. For the samedesign premises, an amount of 22 MW of electric power must beimported from the grid for the backpressure/extraction steamturbine conventional cycle, and an electric self-sufficiency is ob-tained for the condensing/extraction steam turbine conventionalcycle.

Economic results were also considered and BLGCC configura-tions presented payback 4.1 and 5.4 years, respectively, for withoutand with CO2 capture system. The cost of electricity, however, wasalways attractive for all considered scenario. Payback of 4.1 and 5.4years are considered high for private investors and actual carboncredit does not contribute for a better economic result in this case.

or a variable percentage of initial investment.

Fig. 8. COE e cost of electricity considering a variable percentage of initial investment.

Fig. 7. Internal rate of return of BLGCC configurations for a variable percentage of initial investment.

Fig. 9. Cost of electricity against operational hours for BLGCC configurations.

E.T.F. Ferreira, J.A.P. Balestieri / Applied Thermal Engineering 75 (2015) 371e383382

E.T.F. Ferreira, J.A.P. Balestieri / Applied Thermal Engineering 75 (2015) 371e383 383

Acknowledgements

The first author is indebted to Brazilian Electricity RegulatoryAgency e ANEEL (process PD-0553-0022/2012) for his doctorategrant. The second author is indebted to the National Council forScientific and Technological Development (CNPq) for his produc-tivity grant (process 302939/2011-3), to S~ao Paulo Research Foun-dation (FAPESP, process 2013/07287-3), S~ao Paulo State UniversityFoundation (FUNDUNESP, process 1908/009/13-PROPe/CDC), andBrazilian Electricity Regulatory Agency e ANEEL (process PD-0553-0022/2012). The authors are indebted to an anonymous reviewerwhose advices improved substantially this work and to EduardoFranzoni Guilherme for his valuable information about black liquorcomposition.

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