| If the long-distance pipeline is not completely dried when it is put into operation,the water content of the gas entering the city gate station will increase,gas with high water content is easy to condense out liquid water during pressure regulation,the hydrate may form and block the valve,bringing great safety risks.In this paper,according to the hydrate block of a city gas gate station from 2017 to 2018,the hydrate formation conditions were predicted according to the Ng-Robinson model,the effects of methane,ethane,propane and iso-butane on hydrate formation conditions were analyzed,the effects of changing the mole fractions of methane,ethane,propane and isobutane on the hydrate formation conditions were compared.The calculation results show that the changes in isobutane and propane contents have a significant effect on the hydrate formation conditions,the methane and ethane contents changes have little effect on hydrate formation conditions;Comparing the accuracy of calculating the hydrate formation temperature between the Chen-Guo model and the Ng-Robionson model,the Chen-Guo model has higher accuracy;The temperature drop law during natural gas throttling was studied,and the accuracy of the temperature drop calculated by BWRS,PR,SRK equation in HYSYS was compared.Among them,the calculation accuracy of BWRS equation was the highest,and the calculation results of SRK equation and PR equation were close.The PR equation and SRK equation in HYSYS are used to calculate the saturated water content of natural gas,and the results are compared with the experimental data.The results show that the PR equation is more accurate than the SRK equation;Using the PR equation to compile the program which can realize the conversion of water dew point and water content.Compared with the calculation result of the PR equation selected in HYSYS,the error of the water content calculation is between 1.19~2.90mg/m3,the error of water dew point calculation is between 0.1 ~0.6 ?,verify the accuracy of programming calculation.Combined with the actual operating conditions,the possibility of hydrate formation during natural gas pressure regulation was analyzed.The MEOH / EG concentration required to prevent hydrate was calculated using HYSYS,methanol is 33.1% ~ 49.8%(wt),ethylene glycol is49.1% ~ 65.9%(wt).The total injection volume is calculated,methanol is 2.42 ~ 3.05L/ 104Nm3,ethylene glycol(80% wt)is 0.40 ~ 1.79 L / 104Nm3,the heating power for preventing hydrate is calculated.The economics of the three control schemes are compared,the total cost of the heating scheme is the highest,and the economics of the methanol and ethylene glycol schemes vary with the temperature before throttling.The user interface is developed based on Matlab,which can predict the temperature drop of throttling process through the BWRS equation,calculate the hydrate formation temperature through the Chen-Guo model,and use the improved PR equation in HYSYS to determine whether there is water condensation in the throttling process,calculate the maximum value of water dew point to ensure no water condensation during throttling,the methanol concentration required for the prevention hydrates and the amount of methanol injected can be calculated,the comparison results are close to HYSYS,and the absolute error is 0 ~ 0.09 L / 104Nm3. |
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