Study On Synthesis Material Recovery Of Vent Gas From F-T Synthesis

National energy safety is seriously threatened by increasing degree of dependence on foreign petrol,highly centralized imported sources of oil,single transportation mode and acute fluctuation of the international oil's price,which force our country to construct petrol security strategy system.To establish the technical reserve of synthesis oil technology by F-T synthesis could effectively ensure national petrol strategic security.The Inert gas such as N₂, Ar,CH₄ et al could accumulate during synthesis process.So the concentration of the inert gas increases gradually,which could decrease the partial pressure of reactants,affect the balance of the F-T synthesis reaction,and reduce the conversion rate of raw materials.Synthesis system must exhaust a certain amount of vent gas in order to control the concentration of the inert gas.The vent gas usually as fuel gas imports the fuel pipe network,which decrease the value of vent gas.H₂ and CO recovered from vent gas could directly return to the synthesis device due to the vent gas doesn't contain catalyst poison gas,so recovery H₂ and CO from vent gas could effectively reduce the unit consumption of synthesis product,increase the economic benefit of recovery process and product competition.According to the characteristics of vent gas's pressure and composition,this paper proposed the integrated recovery process composed of membrane separation and PSA. Unisim Design software is utilized to simulate the recovery process of membrane modules prepared by PSf and PI.The effects of product hydrogen concentration and pressure in the permeate on hydrogen recovery rate and economic benefit have been discussed.The initial condition of hydrogen recovery is choosing membrane module made from PI with one-stage recovery process,and 100kPag as the pressure in the permeate.The entrance pressure of PSA is determined according to the pressure of fuel pipe network and CO as the adsorbed gas,and the PSA-CO recovery process adopts 5-1-1/RP VPSA technique.In the whole process,the recoveries of H₂ and CO are 89.0%and 83.4%respectively,the economic benefit is 3.77 billion yuan per year and the investment payback period is 15 months.The integrated recovery process has been optimized according to the recovery process characteristics and components of material flow exhausted from process.First,the process economic benefits of the CO purging membrane module and H₂ purging PSA have been compared and the process of H₂ purging PSA is the better scheme.The processes of adsorption tail gas recovery and replacement gas recovery have been discussed on above basis. The results show that replacement gas recovery process has higher economic benefit,about 3.87 billion yuan per year in present prices of synthesis gas and fuel gas,the recoveries of H₂ and CO are 89.0%and 93.5%respectively and the investment payback period is 15 months. The maximum capacity and stability of recovery process have been discussed,the results show that the maximum capacity is 1.2 times as much as the designed capacity.In the condition of present prices of membrane modules and synthesis gas,whenαH₂/N₂ is less than 95,the economic benefit of membrane modules replacement is higher.The product hydrogen concentration is greatly affected by CO₂ concentration of vent gas,but the effect ofαCO₂/N₂ on hydrogen recovery process can be neglected.The pressure drop in hollow-fiber membrane is necessary factor in actual application. Membrane Extension module of Unisim Design has been improved because the pressure drop in hollow-fiber membrane was neglected in the initial module.Improved module adds parameters such as inner diameter,external diameter and length of hollow-fiber membrane. Module adopts differential calculation equations and four-order Runge-Kutta method. Improved module compared with initial module could obtain calculation results that are more close to experimental values.