Study The Effect of The Main Variables on The Objectives of The Natural Gas Dehydration Plant by ASPEN-HYSYS v8.8

In the NGD process, TEG dehydration is commonly employed to prevent corrosion and blockage of equipment, valves, and piping systems. TEG is frequently lost in the system during this procedure owing to vaporization and carryover. Therefore, it is necessary to study the affection of variables of the dehydration process the process was simulated with ASPEN-HYSYSV8.8 and the thermodynamic model was glycol-package; the process was validated by comparing the Plant results with the simulation results and demonstrating good acceptance. ASPEN-HYSYS conducted a sensitivity study to investigate the impact of variables on the main objectives. , as this study showed that not all of these variables have a strong effect, some of them have a weak effect, for example (wet gas pressure and same case of solvent pressure) and the rest of the variables have a strong effect on this process, so it must be taken into consideration by the station operators where this The changes were targeted because they are subject to change within the plant, and the highest value and the smallest value were taken according to the factory's parameters. As these variables are taken into account and the requisite improvements are made, the natural gas drying process will improve, and the dry gas requirements needed will improve, resulting in increased benefit.

causing an increase in operating pressures and the risk of equipment damage due to liquid carryover, As a result, it is important to prevent liquid water and hydrocarbons from condensing [2]. The presence of moisture in natural gas can lead to issues like hydrate formation or freezing, which can lead to pipe plugging, corrosion, and a decrease in combustion efficiency [3].
As a result, the gas needs to be dried. Dehydrating natural gas can be done in a variety of ways, including: Using a solvent to absorb [4], Cooling [5], Adsorption [6], Membrane separation [7], and Separation at ultrasonic speed [8]. The absorption with tri-ethylene glycol in the gas dehydration procedure is one of these processes. TEG has strong absorption properties as well as low volatility, making its application more economically and environmentally viable [9].
There are two stages to the procedure: The water is drained from the gas in the first phase in a staged tower (absorption column), and the solvent is regenerated in the second column (distillation tower). After that, the solvent is returned to the first column to extract more water from the feed gas. TEG is normally lost in the system as a result of vaporization or carryover in this phase and the economic matters and another common concern, such as an insufficient TEG circulation rate or high methane content in rich TEG [10], energy obligation intake, and dry gas water concentration [11]. To achieve the permissible water concentration in the gas, minimize the use of energy, and minimize the depletion of TEG, it is important to investigate the effects of multi-variables on the dehydration process. Furthermore, objective functions in most chemical engineering optimization problems are incompatible.
In the dehydration mechanism, for example, minimizing water content and minimizing heat duty are at odds. When the former is minimized in the otherworld, the above is usually maximized. As a result, all objective functions can be viewed at the same time. There are many studies on how to study and improve the gas dehydration process, Ranjbar [12] investigated the use of a relative sensitivity function (RSF) to optimize a domestic TEG dehydration device. RSF resulted in a decrease in the water content of dehydrated gas, TEG circulation capacity, and re-boiler duty.
Rahimpour [13] investigated the Sarkhun gas processing facility's dew point adjustment unit, The multiple separator and filters were simulated using the steady-state simulation program HYSYS, and the optimum separation temperature was calculated as a result. Kamin [11] glycol flow speeds, absorber levels, re-boiler temperature (180 C, 190 C, and 200 C), and stripping gas rate on the water content of the gas, He discovered that increasing the re-boiler temperature above 200 C caused glycol to thermally decompose, and that adding stripping gas had a greater effect than raising the re-boiler temperature.
The research proposal has two main goals. The first is to use the ASPEN HYSYS v8.8 software application to model the natural gas dehydration process for the Basra plant to use it as a case study. Figure 1 depicts the process flow diagram of the Basra plant and displays all of the operating conditions of temperature, pressure, and mass flow for each channel. After that, an inspection of the method was carried out by comparing the actual plant findings as shown in Figure 1 with simulation results data to ensure that the simulation is accurate. The second goal is performing a sensitivity analysis to determine the degree of the effect of the variables (Twgt, Pwgp, Mwgf, TTEG, MTEG, and Trgt) on the objective functions (Wout, Qhd, Ls, and Mdry).

Process description and Simulation
The glycol process is the most efficient and widely used process in the gas industry [15], Triethylene glycol liquid desiccant is used as a solvent in this procedure to extract water vapor from natural gas. Furthermore, glycol solvent has a strong attraction to water vapor [16], NGD is a renewable energy source. Gas dehydration and TEG regeneration are the two main aspects of the dehydration method. The feed wet gas is dehydrated by an absorption tower in the dehydration section, and water is separated from the solvent in the regeneration section; after regeneration, lean TEG is recycled directly to the contactor tower (Absorption).
A dehydration device usually includes the following components: contactor, flash tank, exchangers, scrubber, and distillation [10], to investigate the effects of a TEG process field, you must first simulate a base case ( Figure 1). The glycol kit model was used in an Aspen HYSYS simulation V8.8. The model is better for gas dehydration process simulation because it offers correct water quality, dew point temperature, and activity coefficient calculations. As previously said, the Basra gas dehydration plant is used as a case study (see Figure 1) and is simulated with and the TEG solvent stream, as well as operating conditions and compositions that are identical to the data in this case study (see Figure 1). The simulation setting is reached after completing the above. Furthermore, the simulation environment can take into account the main simulation area, which deals with the process plant and displays the process plant's PFD. It's important to use an inlet gas scrubber to clear any unwanted impurities including liquids and solids. The absorption tower for tri-ethylene glycol is a vital part of the process plant that requires certain requirements, such as stream temperature, pressure, and flow rate as mention in Figure (  The absorption takes place on the contactor or absorber column, which are vessel trays. The wet natural gas reaches the bottom of the tower and the lean TEG glycol enters the top of the shaft.
The upflowed wet gas comes into contact with the lean glycol solvent as it runs down into the trays. The wet gas's water vapor is absorbed by the lean glycol solution, which then escapes from the bottom of the tower as rich glycol. As a dry gas commodity, the gas escapes the top of the column. Furthermore, the rich TEG glycol must be regenerate, which can be accomplished by building a distillation tower, with specifications that must simulate the distillation column seen in

Sensitivity analysis of NGD process
The gas dehydration process model was subjected to a sensitivity analysis to observe the effects of a few key variables, with the aim of identifying these variables as decision variables in the subsequent optimization research on process results. The variables are wet feed gas temperature (T wgt , oC), wet feed gas pressure (P wgp , bar), wet feed gas mass flow rate (m wgf , kg/s), inlet TEG temperature (T TEG , oC), inlet TEG mass flow rate (M TEG , kg/s), and rich glycol temperature (T rgt , oC). To notice the results of contrast on certain measured quantities indicate the process efficiency, the value for each of these variables differed in a predetermined case while others were kept constant. The water content of dried gas ppm, re-boiler heat duty kJ/s, TEG loses, and dry gas flow rate kg/s are the objective functions.
The effect of the wet gas flow rate: According to the sensitivity analysis of the input feed wet gas mass flow (Figure 3Ab). wherein an equation (2) was used, the empirical equation (2) proposed by [2] is as follows: T dew.eq = 18.228 * ln (0.001685 * W out * P g 0.81462 ) ‫ـــــــــــــــــــــــــــــــ‬ (2) Because the dew point is directly proportional to the water content, when the water content drops, so does the dew point [6]. Furthermore, as shown in (Figure 3Ac), when all process plant parameters are fixed and the mass flow rate of wet gas is increased, the tri-ethylene glycol TEG losses are reduced. This is because the solvent flow rate is constant when the sensitivity of this variable is investigated, As a result, when the solvent percentage is divided by the quantity rate kg/s, increasing the wet gas mass flow rate resulted in a drop in water content in the dry gas stream (Figure 3Aa), which led to a reasonably linear fall in dry gas dew point temperature of gas exiting the tower, this value steadily reduces as the gas flow rate increases, with the exception that heat duty consumption rises as the feed wet gas mass flow rate rises, as shown in (Figure 3Ad). The fundamental reason for this is that a larger feed wet gas mass flow rate puts more strain on the process plant system, resulting in higher heat duty consumption. It's only logical that when the wet gas flow rate rises, the dry gas flow rate rises as well, as seen in (Figure   3Ae). quantity for this plant is between (10 -20 kg/s TEG). The number of absorption tower trays affects the TEG solvent flow rate. As a result, the absorber tower requires (6) trays to run at 0.025 m3 TEG/kg water [19], As previously stated, these values are in terms of pure TEG solvent (100 percent mass fraction). When using the ASPEN HYSYS software to investigate the influence of the TEG solvent flow rate on the water content, the findings revealed that raising the TEG solvent flow rate from 10 to 1000 kg/s increased the water content, as shown in Figure 4Ba.
However, this result was not pure owing to the return TEG solvent from the distillation tower (0.918 mass fraction TEG and 0.082 mass fraction water). Because this TEG is pure (100 percent TEG) and this purity is difficult to get, raising the pure TEG mass flow rate from 10 to 100 kg/s reduces the water content percentage until it gets close to zero, as shown in (Figure 3Bb). TEG glycol solvent circulation levels that are too high can create a slew of issues. If this is the case, the device is over circulating the TEG, and lean TEG glycol cannot have enough heat exchangers to be properly cooled, and the resulting dry lean glycol will not be removing water at the appropriate rate. A rapid rate of circulation does not provide enough time for the hydrocarbons in a phase separator to settle, which can result in hydrocarbon deposition, glycol loss, foaming, and even pollution. Increased glycol circulation levels can also result in an increase in the re-heat boiler's demand. Over circulation also adds to increased air pollution since emissions are proportional to the rate of circulation. Under circulating the TEG solvent gives inadequate quantities of TEG for the amount of water to be extracted in the absorber and resulting in Wet Gas Marketing. In view of the above, leans TEG glycol flow rate must be targeting and study the affection of variables on it, where this can be achieved by testing the moisture of the treated gas dew point temperature [20]. As shown in Figure 4Bc, increased solvent flow results in larger TEG losses. This is due to the fact that an excess of the solvent causes an increase in evaporation and the possibility of a carryover. In addition, (Figure 3Bd) depicts the affection, in which the increase in energy amounts begins gradually as the TEG solvent rate increases, and it also demonstrates that the flow rate has a substantial influence on heat duty consumption. Due to the solvent's propensity to absorb not only water but also hydrocarbons [21], raising the TEG solvent flow rate results in a drop in the dry gas flow rate (Figure 3Be), and hence the increase results in a drop in output.
shown in Figure 4Ee, as the pressure of the wet gas rises, the dry gas flow rate rises as well, and as can be seen from the curve line, the effect is strong and evident from 30 to 45 bar, and at 46 bar and above, the impact begins to stabilize and the increase is minor. The effect of Rich solvent temperature: As illustrated in section 2, the temperature of the Rich solvent is regulated by the functioning of the Lean glycol/Rich glycol heat exchanger (E-101) (Figure 2). Because it has a huge influence on the distillation tower, especially the boiler of the distillation tower, as shown in Figure (4), rising rich glycol temperature leads to a considerable drop of re-boiler heat responsibilities.

Conclusions
The natural gas dehydration process at the Basra plant was used as a case study in this study, and it was modeled using the Aspen HYSYS V8.8 computer program. The Aspen HYSYS simulator model was successfully verified using design information from a TEG dehydration process; the process was then sensitivity analyzed for four sets of objectives and six primary factors, including water content in dry gas, re-boiler heat duty, TEG solvent losses, and dried gas flow.
Wet gas temperature, wet gas mass flow rate, wet gas pressure, TEG temperature, TEG mass flow, and Rich glycol temperature are among the variables.
A sensitivity analysis of these variables was conducted on the main objectives, as this study showed that not all of these variables have a strong effect, some of them have a weak effect, for example (wet gas pressure and solvent pressure) and the rest of the variables have a strong effect on this process, so it must be taken into consideration by the station operators where this The changes were targeted because they are subject to change within the plant, and the highest value and the smallest value were taken according to the factory's parameters.
T wgt = wet gas temperature C.
M wgf = wet gas flow rate kg/s. P wgp = wet gas pressure bar.
T TEG = TEG temperature C.
M TEG = TEG mass flow rate kg/s. T rgt = rich glycol temperature C.
W out = water content (kilograms of water per million standard cubic meters).
T dew ; is dew point in C. P g = pressure (MPa).