PTQ Q4 2023 Issue

Estimating natural gas demand at a petrochemical complex

A robust model has been developed to predict a plant’s natural gas demand, accounting for fluctuating capacities and anticipated fuel gas and steam consumption/production

Uğurcan Tozar, Mert Akçin, Murathan Bağdat, Dila Gökçe Kuzu, Nesip Dalmaz and Kemal Burçak Kaplan SOCAR Türkiye

P etkim is a petrochemical complex in Izmir, Türkiye, operated by SOCAR Türkiye. More than 10 plants are operating in the complex. Energy sources at these plants consist of natural gas, steam (generated by using natural gas), and electricity. Natural gas is one of the most critical energy sources. Predicting natural gas consumption in a day ahead period has a significant role in preparing nat - ural gas consumption plans. Natural gas is consumed by three main facilities, includ- ing gas turbines, aromatics, and steam generation plants. In the gas turbine, natural gas is combusted to generate electricity and heat. Waste heat is used to preheat the boiler feed water transferred to the steam generation plant. The aromatics plant is also one of the natural gas consumers. Natural gas is mixed with the fuel gas in the plant, and the natural-fuel gas mixture is combusted in the furnaces. The steam generation plant accounts for a significant share of fuel consumption. Steam supplied by this plant to the complex is generated by combustion of the fuel gas, consisting of a mixture of plant-produced fuel gas and nat- ural gas. A detailed process description is mentioned in the energy balance section. The main point with modelling the natural gas demand of the petrochemical complex is based on many operational variables, such as plant capacities and ambient tempera- ture. In this study, the effect of plant capacities on steam consumption is analysed in detail. Fluctuation in natural gas consumption is caused by the change in the ambient temperature. Key aspects of natural gas demand modelling Navigating the complexities of modelling the natural gas demand for such an expansive petrochemical complex involves accounting for numerous operational variables. Key among them are the varying capacities of individual plants and the ever-fluctuating ambient conditions, par - ticularly temperature. This investigative study focuses on the impact of plant capacities on steam consumption. Furthermore, it delves into how meteorological shifts, specifically in temperature, are served as catalysts, inducing ripples in natural gas con- sumption patterns.

Natural gas

Steam generation plant

Aromatics plant

Gas turbine

Figure 1 Natural gas consumers

Energy balance Every single consumer has been modelled by considering specific operational constraints (see Figure 1 ). Gas turbine Natural gas is used by a gas turbine to generate electricity and waste heat. The primary operational constraint affect- ing this equipment’s efficiency is ambient temperature. The consumed natural gas is modelled by considering gener- ated electricity and ambient temperature as dependent var- iables. The electricity load of the turbine is independent of the complex’s energy demand. It also operates approximately 20-60 MWh load by considering the ambient temperature. The electricity gen- eration capacity of the gas turbine is limited by higher tem- peratures, especially those with a high humidity content. In gas turbine systems, a significant portion of the provided energy to the gas turbine is lost as waste heat. In the sys- tem, the boiler feed water used in steam generation is pre- heated by the utilised waste heat. When modelling the energy balance in the gas turbine system, it is known that 40-70% of the supplied energy is lost as waste heat. This approach is employed when opti- mising steam generation systems in the shutdown cases of the gas turbine system. In a shutdown case, the waste heat energy used to preheat the boiler feed water is compen- sated by consuming more energy in the steam generation plant. Steam generation plant (boiler) Steam is used in a petrochemical complex for various heat sources, such as heating and power generation. The pri- mary steam generation source is boilers established in the Petkim Steam Generation Plant. Extra high-pressure steam

PTQ Q4 2023