Gas Dehydration Field Manual docx

[...]... Prevention FIGURE 1-4 Water content of CO2-Sharma FIGURE 1-5 Water content of H2S-Sharma 9 1 10 Gas Dehydration Field Manual FIGURE 1-6 Sour gas correlation—SRK Hydrate Prediction and Prevention 11 Example 1-1: Calculation of Water Content in a Sour Gas Stream Determine: Calculate the saturated water content of a gas with the analysis shown below at 1100 psia and 120 F Composition yi N2 CO2 H2S C1 C2 C3... saturated natural gas mixtures The water content shown in API bbl/MMSCF can be converted as follows: lbm/MMSCF ¼ (350)(bbl/MMSCF) The correlation is a “quick-look” way to estimate sour gas content Effect of Nitrogen and Heavy Ends Nitrogen holds less water than methane Pressures up to 1000 psia (69 bara) water content of nitrogen is 5–10% less than methane 1 8 Gas Dehydration Field Manual FIGURE 1-3... lbm=MMSCF 1 12 Gas Dehydration Field Manual Note that the water content is greater using Equation 1-2 than from McKetta-Wehe plot A value of 116 is not likely but could happen Do not treat any one number as sacred Look at the range when determining water content Applications Correlations are used: In dehydration calculations To determine how much water, if any, will condense from the gas involves considerations... correlation; intersect initial pressure ¼ 4000 and DP-3000 read DT ¼ 80 F 1 18 Gas Dehydration Field Manual FIGURE 1-7 Temperature drop accompanying a given pressure drop for a natural gas stream Hydrate Prediction and Prevention 19 HYDRATE PREDICTION CORRELATIONS Overview All correlations are based on a system that contains only gas and water in a static test cell that was rocked only to provide good equilibrium... Therefore, hydrates will form at 75 F 1.08 0.87 1 24 Gas Dehydration Field Manual FIGURE 1-12 Vapor-solid values for normal-butane Pressure-Temperature Curves (Figure 1-13) Pressure-temperature curves are used when gas composition is not known or for “first approximation.” Graphs have been developed to approximate hydrate formation temperature as a function of Gas gravity Pressure Hydrate Prediction and Prevention... TEMPERATURE AND PRESSURE Wellhead Conditions Temperature and pressure of a gas stream at the wellhead are important factors in determining whether hydrates will form when gas is expanded into the flowlines 1 14 Gas Dehydration Field Manual Temperatures at the wellhead increases as the flow rate increases and the pressure decreases Thus, wells that initially flowed under conditions causing hydrates to... constant, K, for each component where Ki ¼ Yi Xi ð1-4Þ Where: Yi ¼ Mol fraction of each component in the gas on a water free basis Xi ¼ Mol fraction of each component in the solid on a water free basis 3 Calculate the ratio, Yi /Ki, for each component 4 Sum the values of Yi /Ki 1 20 Gas Dehydration Field Manual 5 Repeat steps 1–4 for additional temperatures P until Yi /Ki ¼ 1 Figures 1-8 through 1-12 are... Hydrate Prediction and Prevention 21 FIGURE 1-9 Vapor-solid “K” values for propane Gas streams containing more than 30% H2S behave as if they contained pure H2S Components heavier than butane have Ki ¼ infinity, since their molecules are too large to fit into the cavities of the lattice structure 1 22 Gas Dehydration Field Manual FIGURE 1-10 Vapor-solid “K” values for isobutane Example 1-3: Determination... 33.3 33.4 33.5 - 34.8 35.1 35.4 - 36.2 36.7 37.2 - 37.2 38.0 38.7 - 28.8 39.7 40.5 - 40.6 41.6 42.5 - Flowline Pressure, psig After National Tank Company (1958) Gas Dehydration Field Manual Table 1-2 Specific Heat Factor of 0.7 Specific Gravity Gas Hydrate Prediction and Prevention 17  Table 1-3 Average Ground Temperatures (Tg), F Cover, in Tg,  F 36 18 53 to 58 25 to 45 (Northern Europe, Canada, Alaska)... Temperature Using Pressure-Temperature Correlations Given: A 0.6 specific gravity gas operating at 2000 psia Solution: From pressure-temperature curve intersect 2000 psia and 0.6 specific gravity curve and read 68 F HYDRATE PREVENTION Overview Hydrate prevention is used to prevent hydrates from forming 1 26 Gas Dehydration Field Manual Operating conditions must remain out of the hydrate-formation zone Hydrate .