Flash Process Simulation And Flash Gas Recovery Technology Study On High Sulfur Natural Gas Purification Plant

In recent years, increasing production of Puguang gas field leads to high sulfur natural gas processing plant equipments at full capacity or overloaded. Flash gas generated by integrated units is far more than design value, a large amount of flash gas is directly incinerated as waste through exhaust incinerators, causing the exhaust incinerator overloaded, or even shut down, so most of the flash gas are emptied by low-pressure through the torch, which not only affects production, but also results in waste of resources and environmental pollution.This topic is focused on Puguang to deal with flash gas problem of high sulfur natural gas processing plant. Depending on Aspen HYSYS to establish acid gas removal and dehydration model, in use of the "Databook" analysis function to obtain the effects of the main parameters on of purifying, flashing and regeneration results. For acid gas removal unit: with the imported raw materials temperature of absorber increases, the absorption effect reduces; with the increasing of the lean amine temperature, the absorption of CO₂ is promoted while H₂S is inhibited; with the lean amine quantity increases, the absorption effect increases; increase the cooling temperature of interstage semi- rich amine solution and also can promote absorption effect. Increase the inlet rich amine temperature of flash column entrance promotes flash effect, so do the supplementary amine temperature and pressure drop. Reflux ratio increasing contributes to the regeneration of H₂S while inhibits desorption of CO₂, but small changes; rich amine temperature of regeneration tower inlet increasing promotes desorption of CO₂ and inhibits H₂S desorption while the pressure increasing promotes H₂S desorption and inhibits CO₂. For dehydration unit: the adsorber inlet lean TEG amount increasing promotes dehydration effect, while the wet gas temperature increasing reduces it, so does the pressure drop, the lean glycol dehydration temperature and pressure does not affect the results; supplementary TEG quantity increasing promotes flash effect; rich glycol temperature of regeneration tower inlet increasing reduces the regeneration effect, while the reflux ratio is just the reverse, but the change is small; the fuel gas usage of stripper increasing facilitates the regeneration effect, when to a certain amount the result no longer changes. According to these effects we can choose the optimal simulation parameters. Comparison of the optimization model parameters with actual running data shows that the acid gas removal and dehydration model can represent the actual operation of the device well, error is 2%. It shows that the method of optimization of process parameters is feasible.Based on the model to analyze the flash gas influence factors: wherein the flash tower pressure and the supplementary TEG concentration rising, the inlet rich solution temperature and MDEA concentration decreasing all reduce the flash gas amount; the top pressure and supplementary TEG concentration changing shows no effect on absorption effects and CH₄ mole fraction of flash gas, but when bottom pressure increases, the inlet rich solution temperature and supplementary MDEA concentration decrease, the CH₄ content will increase and the acid gas content in flash gas decrease.Depending on analysis of both energy consumption and investment, select the best low-pressure purification process. According to the actual situation of plant and gas characteristics, choose equipments and purification process. Using two 13 X molecular sieve towers to purify gas, adsorption and regeneration cycle period are both 8 hours. The amount of required molecular sieve in one period is 26254 kg, diameter of molecular sieve adsorption tower is 2.0m, and height of the bed is 16 m.The process can recover flash gas as an amount of 2761.6×10⁴m³Nm³/a, and can achieve 44.296 million Yuan and is to cover the cost in 6 monthes. It shows that flash gas recovery has seen a good economic benefit.