The Modeling And Evaluating Of Dual-gas Polygeneration System

The polygeneration system, which producing liquid-fuel combined with electric power, has the advantage of high energy efficiency and low pollutant emission. It is an effective way of solving liquid-fuel shortage and environment pollution struggling by China. Dual-gas polygeneration system, feeding by the coking-oven gas and the gasified gas, made good use of coking-oven gas in China, and also get the maximum element utilization through the reforming of methane and carbon dioxide.Process simulation software Aspen Plus was used to set up the dual-gas polygeneration system, which including air separation unit, coal gasifier, CH₄/CO₂ reformer, liquid phase methanol and DME synthesis reactor, product separation unit, gas turbine combined cycle. The CH₄/CO₂ reforming, liquid fuel synthesis were programmed by the kinetic subroutine to satisfy the chemical reaction process in the units. The principle of system calculation of both thermodynamic and kinetic equilibrium are based on mass and energy balance. The simulation results of these units were consistent with the experimental data which were collected from reference literature.Based on the simulation model of DME as end-product, the methanol equivalent yield, DME productivity and conversion of CH₄+CO₂ were used as the object function to optimize the operation parameters of the individual units mentioned above. The optimizated operation parameters of each unit and flow ratio of coking-oven gas to gasified gas are acquired. Furthermore, the two kinds of flowsheet, one-step and two-step DME synthesis process, were compared by the methanol equivalent yield, and the synergetic effect in the one-step DME synthesis process was investigated. The results of optimized temperature, pressure, space velocity of CH₄/CO₂ reformer are 900℃,1atm, 3000 L·h^-1·kgcat^-1. The results of optimized temperature, pressure, space velocity of DME synthesis reactor are: 260℃, 6MPa, 5000 L·h^-1·kgcat^-1, the optimized flow ratio of coking-oven gas to gasified gas is 0.875.After we got the optimizating operation parameters, three kinds of dual-gas polygeneration were design and modeling. Equivalent electric power efficiency which considers the energy quality was calculated based on the modeling platform. The results show that the equivalent electricity is more reasonable for the dual-gas systems. These systems were compared by electric power efficiency and CO₂ emission, the result showed that the polygeneration which main product is DME including CH₄/CO₂ reforming is the optimized process.