Abstract:

During the transportation of the natural gas gathering station, due to the constantly change of the temperature and pressure, it is easily to occur the hydrate, resulting in the clogging of the pipeline and affecting the normal transportation of natural gas. The main way is injecting the methanol when the natural gas by the gathering station. According to the situation of Zizhou gas gathering station, we used the process model of "the separation at room temperature in small station, transportation as moisture vapor, and concentrated dehydrocarbon and dehydration in processing plant". In order to determine the reasonable methanol injection quantity and optimize the methanol injection system, firstly, we measured and compared the water dew point and the ambient temperature of the natural gas at the inlet and outlet of the separator at each level to determine whether methanol injection is needed. If the methanol was needed, we would take the maximum difference calculated between the gas dew point at each stage of the gas separator and receiver, and the corresponding ambient（pipeline） temperature as the maximum temperature difference that need to be optimized. Then, we used the industry standard dew point correction chart to establish the dew point correction model. Finally, based on the maximum temperature difference to be optimized, we determined the optimum methanol injection amount by the correlation analysis between the methanol injection volume and the temperature correction value in the gas gathering station of Zizhou gas field. The obtained methanol injection volume can effectively inhibit the formation of hydrate and save the cost. The final recommended table for methanol injection volume suitable for the gas gathering station in Zizhou gas field can be used to guide the production.

Key words: optimization of methanol injection quantity, gas gathering station, water dew point, natural gas hydrate, temperature correction