Evaluation of Newly Designed Polygeneration System with CO₂ Recycle

Abstract

A new coal-based polygeneration system with CO 2 recycle is proposed in this paper. With the gasified coal gas containing 23 vol % CO 2 and the coke oven gas containing 25 vol % CH 4 as the dual gas sources, the system mainly produces methanol, dimethyl ether, and electric power. The system adopts CO 2 /CH 4 reforming to modify the C/H ratio of the syngas. Particularly, the CO 2 , coming from the distillation tower, is recycled separately back to be a reactant during gasification and the resource gas in the reforming unit. As the CO 2 concentration in the exhausted gas from the distillation tower is more than 95 wt %, this system does not require a CO 2 separation unit. The system avoids the conventional water−gas shift reaction that is used to adjust the ratio of C/H in the syngas, but fully uses the CO 2 produced from coal gasification, which solves the problems of CO 2 capture and storage. The performance of the whole system's energy, CO 2 emission, and economics are analyzed by Aspen Plus 11.1 and Aspen Icarus 11.1 software. Results indicate that the new system realizes 11.5% increase of chemical energy, 1.3% increase of internal rate of return and 33.8% reduction of CO 2 emission at the expense of 8.4% of power output. Especially, the new system can save about 13−18% on energy versus single product systems. The scheme in which CO 2 is recycled back to the gasifier and the reforming unit plays the most significant role in the comprehensive evaluation of energy utilization, CO 2 emission control, and economy benefits of the system.

A polygeneration from a dual-gas partial catalytic oxidation coupling with an oxygen-permeable membrane reactor

“…The PR-BM method is used for the global method. However, the individual property method BWRS is used for DME synthesis subsystem, in which the reaction takes place at high pressure and the feedstocks are hydrocarbons [17]. The Gibbs reactor block is used for simulating gasifier, and the corresponding reaction equations are entered and the deviation from equilibrium is taken into account via approach temperatures.…”

“…The other processes such as separation, compression and heat exchange can be modeled successfully by using Flash, Sep, Heater, Heatx, Compr and Mcompr blocks. The detailed modeling for model selection of each process, process assumption and property methods can be found in previously published study by our group and literatures [17,36,39]. Table 2 shows modeling description for the key units.…”

“…Compared with a conventional process of methanol synthesis from natural gas, the new process has been proved to be superior to the conventional process from the perspective of environment, raw material exploitation and purification costs, and also consumes less energy than conventional production. Yi et al [16,17] designed and estimated a polygeneration system for producing MeOH/DME/electricity from COG reforming with CGG, and it is found that the polygeneration system shows better performance in terms of energy efficiency, economy and CO 2 emission compared with the stand-alone production. Similarly, Lin et al [18] proposed a new polygeneration system for methanol and power production based on COG reforming of CGG with CO 2 recovery, and the new system presents good thermal performance and CO 2 is also avoided with less energy penalty.…”

“…Then, the cooled gas enters the high temperature desulphurization unit in which H 2 S and COS are firstly reduced to 70 ppm in the thickdesulfurization tower, and the rest H 2 S and COS are removed in the fine-desulfurization tower. The concentration of (H 2 S + COS) in the final clean gas reaches below 1 ppm, which makes the adverse effects of sulfur on the CH 4 reforming catalysts and DME synthesis catalysts in the subsequent process efficiently avoided [17]. Next, the clean CGG mixed with purified COG enters the oxygen-permeable membrane reforming reactor where partial catalytic oxidation of COG reaction takes place.…”

Combining coal gasification, natural gas reforming, and external carbonless heat for efficient production of gasoline and diesel with CO2 capture and sequestration

“…They achieved a total plant thermal efficiency 62.8% (HHV) by using an optimal ratio of 0.56 for the rate of coke-oven gas to coal gasified gas. They also proposed a novel dual feed system (coal-coke oven gas) with CO 2 recycle to the gasifier to increase the carbon conversion and decrease CO 2 emissions [29]. Li et al [28] examined a similar system using a combined biomass-natural gas feedstock to get 9% fuel input saving compared with individual systems which use either biomass or natural gas as resource for methanol/power production.…”