Environmental Impact Assessment of Asaluyeh Gas Refinery Products Based on Blue Water Footprint Measurement

1.1. Natural Gas and Processing

Natural gas is unquestionably a significant source of energy in the 21st century, marketed to both domestic and global markets after extraction and refining. The Fifth Refinery of South Pars, Asaluyeh, Iran, produces six byproducts of natural gas: Methane, ethane, propane, butane, gas condensate, and sulfur, and distributes them in domestic and international markets (9).

Raw natural gas, extracted from underground gas fields, is entirely different from the natural gas consumed at residential and commercial premises. Unprocessed natural gas is primarily composed of light and heavy hydrocarbons (${\displaystyle C_n{H}_{2n+2}}$), including methane, ethane, propane, butane, and pentane. It also includes non-hydrocarbon impurities such as carbon dioxide (CO₂), carbon monoxide (CO, hydrogen sulfide (H₂S), nitrogen (N₂), and water vapor (H₂O).

In addition to purifying it and extracting sulfur, natural gas processing entails a series of complex operations that produce byproducts such as ethane, a petrochemical feedstock, and gaseous liquids such as Liquefied Petroleum Gas (LPG) and condensate, which are exported, as well as methane, which is consumed as natural gas (Figure 1) (5, 9, 10).

Figure 1.

Schematic view of the refinery product process route

Natural gas processing, to produce high-quality byproducts for transmission and consumption, is divided into four stages in the majority of natural gas processing facilities:

(1) Condensate removal

(2) Gas sweetening- H₂S and CO₂ removal

(3) Gas dehydration

(4) NGL extraction and fraction

Aside from the four stages mentioned, wellhead equipment such as segregators for separating water from gas, filters for removing sand and other large impurities, chemical injection equipment for injecting corrosion inhibitors, and injecting gaseous hydrates inhibitors are also used (gas hydrates are crystalline solid formed of water molecules and gas molecules trapped inside it. The formation of this crystalline solid has the potential to obstruct the transmission pipeline) (5, 11).

Assessing and quantifying environmental impact is one of the applications of the Life Cycle Assessment (LCA) method. Since the governing approach of an LCA is a cradle-to-grave approach, all different stages of implementing a process or producing a product, from raw material extraction to end of life, are studied (Powell, 2000). In some cases, however, this assessment takes place as cradle-to-gate as the initial part of the cycle or as gate-to-gate as the middle part of the life cycle assessment, which refers to the boundary of the system selected for the assessment of processes or products (12, 13).

According to the standard of the International Organization for Standardization (ISO), an LCA consists of four stages in general:

(1) Goal and scope definition

(2) Inventory analysis

(3) Life cycle impact assessment

(4) Interpretation of results (7, 8, 14).

The water footprint for gas refinery products was estimated using the steam indicator for each processing unit and measuring the amount of makeup water and freshwater consumption in critical stages of processing each product.

3.1. Study Area

The fifth gas refinery, or phases 9 and 10 of a large refinery complex with 24 phases and 14 refineries operating in Asaluyeh Port, was selected as the study area. The gas refinery comprises product preparation processing units, non-processing units (support), and joint units for electricity and steam generation.

Methane, ethane, propane, butane, gas condensate, and sulfur are products of every gas refinery, as depicted in Figure 2, which summarizes the production process (9, 15).

Figure 2.

Simplified diagram of refinery units

The refinery's input feed, which travels through two 32-inch pipelines, first arrives at Unit 100, also known as the facilities unit, where the three-phase inflow fluid (gas, liquid, and solid) is separated. Also known as the gas sweetening unit, Unit 101 is for separating H₂S and CO₂. In fact, sour gas is known as such because it contains the toxic gas H2S. A chemical known as methyl diethanolamine (MDEA) is used in this unit for gas sweetening. This chemical can react with and absorb H₂S and CO₂. Unit 101 of the gas train unit receives its feed from Unit 100, after which water and mercury are separated from sweet gas in Unit 104 (Unit 101) (11, 15).

Unit 105 separates ethane for use as feed in petrochemical units. This unit also produces methane gas, which is known as sale gas, in addition to ethane. This gas is sent to Unit 106 and then to the national gas line, where it will be used as natural gas in domestic pipelines. Natural gas liquid (NGL) refers to heavy gas phases or NGL cuts. Unit 107 (NGL fractionation) receives these products and separates propane from butane. Ethane is routed to Ethan Treatment and Dring Unit 116 for sweetening and devolatilization. Under surface-controlled flow, hydrocarbon liquids are mixed at the bottom of the de-ethanizer tower in Unit 107 and transferred to the de-propanizer tower 101-C-107. Propane and butane are derived from Units 115 and 116. The heavier cuts of fluid containing C⁺⁵ hydrocarbons are then sent to Unit 103, also known as the gas condensate stabilization unit, for separation.

After condensate is produced in the Facilities Unit (Unit 100), inflowing gases from offshore lines must be treated in three phases. The regenerator tower in the sweetening unit (Unit 101) produces acid gas. It is impossible to burn these gases due to environmental regulations and standards. Thus, removing H2S from these gases is critical, which is accomplished in the Sulfur Recovery Unit (SRU). During the production process in Unit 108 of the gas refinery, sulfur is first produced in a molten state and then as granules. Unit 102 is a glycol regenerator unit that has a critical role in maintaining a fuzzy fluid balance and preventing crystalline hydrates of gas fluid from forming inside pipelines. Thus, water consumption in this unit is essential to the production process (5, 9, 11).

This study analyzed the environmental impact of the selected refinery from resource extraction to final product by considering the software performance unit for producing one ton of product. The production rates of refinery products and the annual consumption of electricity and natural gas as the primary feed were collected from the refinery website. Moreover, the necessary calculations were performed to prepare data for entry into the software (Table 1). SimaPro 9.2, which includes Ecoinvent 3 database, was also employed to collect data on the life cycle of electricity generation and other inputs. Including eight environmental impacts such as acidification, eutrophication, global warming, photochemical oxidation, abiotic-element resource depletion, fossil fuel resources depletion, water scarcity, and ozone layer depletion, EPD 2018 was also used in the impact assessment phase (5, 8, 11).

5.1. Environmental Impact Assessment of Methane Production

To produce one ton of methane, approximately 2.6 kg of SO₂ was emitted, responsible for the acidification of the environment. Eutrophication impact in the production of this product was 0.47 kg, which was equal to ${\displaystyle {PO}_4^{--}}$. The environmental impact concerning global warming was 590.60 kg of CO₂. In addition, the photochemical oxidation impact was 2.23 kg of non-methane volatile organic chemicals. As a result of methane production, fossil fuel sources were depleted by 44101 MJ. There was a 5.8239 m³ water shortage (Table 3).

5.2. Environmental Impact Assessment of Ethane Production

To produce one ton of methane, approximately 2.4 kg of SO₂ was emitted, responsible for the acidification of the environment. Eutrophication impact in the production of this product was 0.44 kg, which was equal to ${\displaystyle {PO}_4^{--}}$. The environmental impact regarding global warming was 547.27 kg of CO₂. In addition, the photochemical oxidation impact was 2.07 kg of non-methane volatile organic chemicals. As a result of methane production, fossil fuel sources were depleted by 40866 MJ. There was a 7635.14 m³ water shortage (Table 4).

5.3. Environmental Impact Assessment of Propane and Butane Production

To produce one ton of methane, approximately 4.1 kg of SO₂ was emitted, responsible for the acidification of the environment. Eutrophication impact in the production of this product was 0.73 kg, which was equal to ${\displaystyle {PO}_4^{--}}$. The environmental impact concerning global warming was 912.129 kg of CO₂. In addition, the photochemical oxidation impact was 3.45 kg of non-methane volatile organic chemicals. As a result of methane production, fossil fuel sources were depleted by 68110 MJ. There was a 12725.2 m³ water shortage (Tables 5 and 6).

5.4. Environmental Impact Assessment of Butane Production

All environmental parameters were identical to those used in the production of one ton of propane; therefore, the amounts were not repeated.

5.5. Environmental Impact Assessment of Gas Condensate Production

To produce one ton of methane, approximately 5.1 kg of SO₂ was emitted, responsible for the acidification of the environment. Eutrophication impact in the production of this product was 0.92 kg, which was equal to ${\displaystyle {PO}_4^{--}}$. The environmental impact regarding global warming was 16.114 kg of CO₂. In addition, the photochemical oxidation impact was 4.31 kg of non-methane volatile organic chemicals. As a result of methane production, fossil fuel sources were depleted by 85137 MJ. There was a 15906.5 m³ water shortage (Table 7) (11, 24).

5.6. Environmental Impact Assessment of Sulfur Production

To produce one ton of sulfur, approximately 0.8 kg of SO₂ was emitted, responsible for the acidification of the environment. Eutrophication impact in the production of this product was 0.147 kg, which was equal to ${\displaystyle {PO}_4^{--}}$. The environmental impact concerning global warming was 182.42 kg of CO₂. In addition, the photochemical oxidation impact was 0.7 kg of non-methane volatile organic chemicals. As a result of methane production, fossil fuel sources were depleted by 13622 MJ. There was a 2545 m³ water shortage. The amount of ozone layer depletion gases was 8.12 kg of chlorofluorocarbons (CFC) for producing one ton of ethane in the gas refinery (Tables 8).

The results of each product's evaluation are presented separately in Figure 3. Figures 4 and 5 show a general comparison of each environmental parameter with all of the produced products.

Figure 3.

(A) Environmental impact assessment of producing one ton of methane; (B) Environmental impact assessment of producing one ton of ethane; (C) Environmental impact assessment of producing one ton of propane; (D) Environmental impact assessment of producing one ton of butane; (E) Environmental impact assessment of producing one ton of gas condensate; (F) Environmental impact assessment of producing one ton of sulfur (13, 25, 26).

Figure 4.

Contribution of production of each gas refinery product to acidification, eutrophication, global warming, photochemical oxidation, abiotic-element resource depletion, fossil fuel resources depletion, and water scarcity

Figure 5.

(A) Impact of producing gas refinery products on acidification; (B) Impact of producing gas refinery products on eutrophication; (C) Impact of producing gas refinery products on global warming; (D) Impact of producing gas refinery products on photochemical oxidation; (E) Impact of producing gas refinery products on the depletion of abiotic elements; (F) Impact of producing gas refinery products on water scarcity; (G) Impact of producing gas refinery products on ozone layer depletion (22, 27, 28).