Development of Multimode Gas Fired Combined Cycle Chemical-Looping Combustion Based Power Plant Lay-Outs

72 Operation of power plants in carbon dioxide capture and non-capture modes and energy penalty or energy 73 utilization in such operations are of great significance. This work reports on two gas fired pressurized chemical- 74 looping combustion power plant lay-outs with two inbuilt modes of flue gas exit namely, with carbon dioxide 75 capture mode and second mode is letting flue gas (consists carbon dioxide and water) without capturing carbon 76 dioxide. In the non-CCS mode, higher thermal efficiencies of 54.06% and 52.63% efficiencies are obtained with 77 natural gas and syngas. In carbon capture mode, a net thermal efficiency of 52.13% is obtained with natural gas 78 and 48.78% with syngas. The operating pressure of air reactor is taken to be 13 bar for realistic operational 79 considerations and that of fuel reactor is 11.5 bar. Two power plant lay-outs developed based combined cycle 80 CLC mode for natural gas and syngas fuels. A single lay-out is developed for two fuels with possible retrofit for 81 dual fuel operation. The CLC Power plants can be operated with two modes of flue gas exit options and these 82 operational options makes them higher thermal efficient power plants. 83 (IGCC) Pressurized CLC show higher thermal efficiency and there has been possibility of operating in both CCS and non CCS modes. Jin and Ishida Abad et Adanaz studied on kinetics of oxygen carriers in pressurized CLC environment in lab scale. These results cannot be used to scale-up reactor but these show kinetics in 1 to 15 bar range CLC system will be feasible in case of heavy duty CLC reactors. These studies shows operating CLC based units with high thermal efficiency without much energy consumption for air separation with the feasibility of handling flue gas in CCS and non-CCS mode. balances thermodynamic and syngas.

.57 % and CLC atmospheric and CC CLC is respectively 43.11% and 51.94% after incorporating energy 162 penalty for CO2 compression to 110bar. Though state of art has been illustrated in these technologies with 163 technical maturity (Wall 2007), many of these involves energy penalty in CO2 capture. Energy penalty for coal 164 based, post capture and compression is 12%, oxyfuel combustion capture is 11.2%, IGCC Shell is 9.4% and 165 NGCC post combustion capture is 5.8 % (Davison and Thambimuthu, 2009

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The principle of pressurized chemical looping combustion is shown in Figure 1. Here, the fuel combustion is 216 split in two stages. Firstly, a solid metal (in a low oxidation state, denoted as MeOx-1) is oxidised by oxygen in 217 the air to form metal oxide (completely oxidized state, denoted as MeOx) in air reactor. In the later stage, the 218 metal oxide gives oxygen to react with the hydrocarbon fuel during fluidization to form carbon dioxide and 219 water vapor in fuel reactor. Two stage combustion of fuel by reactor systems eliminates oxygen separation unit 220 and avoids mixing of N2 with flue gas. The exit gases from CLC reactor system are taken through gas turbines 221 followed by heat recovery steam generators to generate power and CO2 separated from the flue gas upon cooling 222 sent for compression.

223
Pressurised operation of CLC reactor systems enables combined power cycles operated under gas turbine as per 224 Brayton cycle and steam turbine as per Rankine cycle to get improved net thermal efficiency of power plant 8 (Kehlhofer, 1999;El-Wakil, 2010). In recent years, pressurized CLC is gaining importance from the researches 226 in the view of reactor configuration, solid-gas contact, reaction kinetics, fuel conversion (

244
Cooled depleted air let to atmosphere. Exhaust gas containing water vapor is separated CO2 upon cooling in flue 245 gas conditioner and more than 95% pure CO2 is compressed to a pressure of 110 bar for sequestration. Two carrier. The nickel oxide flow rate calculation is made by considering 25% excess oxygen supply to fuel in fuel 9 reactor. The CLC-reactors are assumed to be adiabatic with isothermal and homogenous mixing of solids with 255 gases. Air flow rate is calculation is considered in air reactor with an `~ 220% of an excess air. Considering 256 major components of the natural gas and syngas fuels, and their reaction with NiO is given as per reactions (1),

257
(2) and (3) respectively with excess oxygen (   NiO . The term ∆H Red is heat of reduction in kJ/mol i.e., heat absorbed during the natural gas oxidation or NiO 285 reduction. Ni oxidation is exothermic reaction and therfore the term ∆H Ox associated with molar mass is with 286 plus sign as given in Eq. (5) and NiO reduction in fuel reactor is endothermic for the natural gas fired case and 287 thus the term ∆H Red associated with molar mass is with minus sign as given in Eq. (6) and same will be become

384
Mass and Energy balance model is same as already presented in Section 3.1.1 for pressurized CLC with natural 385 gas as the fuel has been used to determine the furnace side parameters for syngas firing. Since syngas has 386 higher cost of compression of CO2, the lay-out has been designed for a 800 MWth, which amounts to 71.43 kg/s 387 of syngas flow and is 4.6 higher than the flow rate of natural gas required for a 761 MWth plant. On the furnace 388 side, the principal sub-systems considered are the air reactor and its preheater, the fuel reactor and its preheater, 389 the gas turbines used to extract power from these exhausts and the compressor to supply air to the air reactors as 390 well as coolant air to the air turbine. Syngas is assumed to be available under pressurized conditions and the 391 cost of its compression is not included in the analysis. As in the case of syngas, the air reactor is fixed to 392 operate at 13 bar and 1200°C, and the fuel reactor is fixed to operate at the pressure of 11.6 bar (at 1226°C).

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The same oxygen carrier is used and its flow rate has been determined for syngas requirements for an 800 MWth  Table 3.

465
Here, a listing is made of the various processes by which power is produced and those by which power is 466 consumed for the four configurations.

467
Overall energy analysis is made for power plant lay-outs and net efficiency for each case is evaluated using Eq. 468 (7) considering the energy penalties for gas compression and water circulation.

496
In order to assess the possibility of dual fuel operation of the pressurized CLC system, a detailed comparison of 497 several parameters associated with the two systems is made Table 4. It can be seen that most of the parameters 498 are fairly similar; the operating temperature of the fuel reactors are slightly different. Due to the exothermicity 499 of the reduction reaction, the fuel reactor temperature is actually higher than that of the air reactor by about 500 26°C with syngas, whereas it is lower by about 50°C in the case of natural gas firing. Another difference 501 between the two fuels is the calorific value and the fuel gas flow rate. Since syngas contains significant amount 502 of CO2 as inert, its flow rate is higher and the flow rate of the exhaust gas from the fuel reactor is also higher.

503
This, coupled with the higher exit temperature of the fuel reactor and lesser gas preheating requirement, results 504 in significantly higher amount of thermal power (105.64 MW for syngas vs 51.71 MW for natural gas) retained 505 in the fuel reactor exhaust gas (see Figure 5 and Figure 8) which is available for powering a Rankine cycle. As 506 can be seen from Table 4, the Rankine cycle for syngas has three turbines (a high pressure turbine (150 bar), a 507 medium pressure turbine (20 bar) and a low pressure turbine (1.7 bar)) while the one for natural gas has a single 508 low pressure turbine with a turbine inlet pressure of 1.7 bar.

509
It can be seen that the major part of the power is produced by the low pressure turbine in the syngas case and 510 that its rating is roughly the same (33,216 kWe to 29,396 kWe) as that of the low pressure turbine in the natural 511 gas case. The air reactor side parameters are nearly similar and there is hardly 5% change in the heat and mass 512 flow rates of various streams. From the above reasoning, it can be argued that except for minor changes in the 513 lay-out for the Rankine cycle parameters, the lay-outs of the syngas-fired and the natural gas-fired pressurized 514 CLC power plants are similar and a unified lay-out is produced in Figure 10. In this common lay-out, natural 515 gas firing requires by-passing of the fuel reactor exhaust from E3 to E6 directly. Correspondingly, the steam 516 side too bypasses the high pressure and the medium pressure turbines and uses only the low pressure turbine.

517
The stream values corresponding to the unified lay-out are given in Table 1 for natural gas and Table 2