Natural gas is considered the cleanest among all fossil fuels with high calorific value and low percentages of impurities. It can be used for industrial and domestic applications as well as power generation plants, either steam or gas power plants. Raw natural gas, primary conditioned, has low cost so it is favorable fuel but not profitable as a commodity, so further treatment and processing should be applied to gain more valuable profit from natural gas. The typical composition of natural gas includes methane, ethane, propane, butanes, pentane and traces of heavier components. All the aforementioned components except methane are called hydrocarbon liquids. These hydrocarbon liquids should be removed from the natural gas not only to meet the assigned specifications to be transmitted safely to the consumers, but their commercial benefit is the major motive to recover them in a greater extent than required for transmission specifications. The hydrocarbon liquids can be divided into two groups: the first group is referred to as natural gas liquids (NGLs) which involve ethane, the desirable component for ethylene production and other petrochemical industries. Propane and butanes are valued as liquid fuel, Liquid Petroleum Gas (LPG), for residential uses or as feedstocks for petrochemical industries. The second group is the natural gas condensate which includes pentane and heavier constituents (C5+) [1]. The condensate is a stable liquid product at standard conditions of pressure and temperature. Moreover, it’s well-known with high API degree because of its light density and high volatility, which results in a valuable product with a premium price over raw natural gas and conventional petroleum crude as well. Fig. (1) shows that the prices of natural gas liquids are ranging from twice to five times of the natural gas prices, which emphasizes the economic importance of hydrocarbon liquids recovery. Hydrocarbon liquids recovery from natural gas can be accomplished by several techniques, depending on the desired degree of liquid recovery, ranging from simple dew point controlling to the complicated technologies that can achieve high ethane recovery. Early in the 20^th century, NGLs recovery processes involved gas compression and cooling accompanied by condensate stabilization. In 1920s, the lean oil absorption technique was introduced to enhance the liquid recovery rich in butanes. Later in 1950s, refrigerated lean oil absorption technique was developed to recover lighter components. The process gas can be refrigerated by different techniques: mechanical refrigeration, expansion through J-T valve, or expansion through turboexpander [2]. NGLs recovery processes with turboexpander are usually recommended because of their high liquid recovery performance [3]. Egypt is on its way to being one of the leading countries in the petroleum refining and petrochemical industries. Natural Gas Liquids (NGLs) are considered the main feedstock for both industries. Egypt experiences a deficiency of NGLs, so it is more profitable to recover NGLs from characteristic gas.

This research is providing a new energy-integrated retrofit for an existing Gas-Oil separation plant in Egypt that was proposed to maximize condensate production. The adopted proposed technique can be considered as surface-enhanced oil recovery from produced gas. The energy-integrated retrofit will be confirmed by its economic feasibility to be conducted to contribute to solving this issue by modification of Gas-Oil Separation Plant (GOSP) located in Egypt to produce the NGLs by following a techno-economic revamping scheme with an energy-saving scope.

Based on the HYSYS 8.8 model of the Gas-Oil Separation Plant (GOSP) of an existing Petroleum Company, which is simulated and verified with the actual data in previous work [5]. A new heat-integrated retrofit is proposed to achieve the maximum recovery of stable condensate (i.e., its Reid vapor pressure (RVP) does not exceed 82.74 kPa). The proposed retrofit is considered a kind of modification in the Gas Subcooled Process (GSP) [6]. The second objective of this research concerns energy savings, which can be achieved by applying pinch analysis for heat integration to determine the targets and design an appropriate heat exchanger network that satisfy the heating and cooling demands. An organic Rankine cycle is introduced as another approach to waste heat recovery and power generation. After environmental and economic evaluations are investigated to determine the carbon dioxide emissions and the profitability of this modification. Finally, results are summarized and compared with their corresponding from the base case and the recommended revamping scheme in previous studies [5].

Fig. (1). Natural gas prices Vs. natural gas liquids prices [4].

From the HYSYS 8.8 Model of the proposed retrofit, shown in figure 2 based on the simulation rules of thumb, it was found that the flow rate of stabilized condensate is directly proportional to the outlet pressure of the compression station reaching the plateau near 6,101 kPa. On the other hand, it decreases dramatically with precooler outlet temperature above -6 ^oC. regarding the RVP of the stabilized condensate, it was found that the critical RVP is about 66.43 kPa at which maximum stabilized condensate production occurs. Figs. (3-6) show that the proposed retrofit, before and after energy integration, achieves the same results in the condensate recovery aspect since it can achieve about a thousand additional barrels per day of stabilized condensate, RVP equals 66.43 kPa, richer in pentanes. As shown in Fig. (7), the energy-integrated model is operating at a moderate pressure of 6,101 kPa with the least compressing power, as shown in Fig. (8), because of utilizing of the generated power from the turboexpander and organic Rankine cycle. As shown in Fig. (9), there is no pinch temperature at the specified ΔT_min, the heating duty can be totally eliminated while the required cooling duty can be reduced to about 3300 kW. The designed Heat Exchangers Network (HEN), which satisfies the targets, is shown in Fig. (10). It was designed to make use of the already-existing air coolers to minimize the tie-ins and complex piping. From Fig. (11), it can be noticed that the designed Heat Exchangers Network (HEN) exhibits a great role in energy saving by reducing the cooling demand by about 14 MW and omit the heating load. Fig. (12) illustrates the direct relation between the heating demand and the amount of carbon dioxide emissions; therefore the energy-integrated model approaches to zero carbon emissions from heating operations. On the other hand, as shown in Table 3, it is considered the least in each cost and the highest profit among the others and reaches the break-even point in less than a year which is favorable in the oil and gas industry.

Fig. (2). The HYSYS model of the proposed retrofit including organic Rankine cycle.

Fig. (3). Comparison of condensate production rate.

Fig. (4). Comparison of additional condensate percentage.

Fig. (5). Comparison of produced condensate RVP.

Fig. (6). Comparison of produced condensate composition.

Fig. (7). Comparison of the maximum operating pressure.

Fig. (8). Comparison of the required compressing power.

Fig. (9). Composite Curves for the proposed retrofit.

Fig. (10). The designed heat exchangers network for the proposed retrofit.

Fig. (11). Comparison of cooling and heating loads.

Fig. (12). Comparison of carbon dioxide emissions released during fired heating.

A new energy-integrated retrofit for an existing Gas-Oil separation plant in Egypt was proposed to maximize condensate production by achieving more than one thousand additional barrels per day of stabilized condensate, which corresponds to a 16.1% increase in percentage, with RVP equals to 66.43 kPa. This proposed technique can be considered as surface-enhanced oil recovery from produced gas. Energy integration played a vital role in decreasing the compressing power by about 31%, the cooling load by about 81%, and totally eliminating the heating load leading to zero CO₂ emissions. The energy-integrated retrofit confirmed its economic feasibility by achieving an annual net profit of about 26.2 million dollars and a pay-back period of one year. To sum up, the new energy-integrated retrofit scenarios exceed the recommended revamping schemes by previous works and base case in all aspects of condensate recovery, energy-saving, environmental concerning and economics.