Scientists from M. Auezov South Kazakhstan University and Tomsk Polytechnical University proved that even standard crude oil treatment and stabilization plants, which have been used for decades practically without any upgrade, still have significant potential for energy saving. During their joint research they analyzed the operation of a field plant with 4 mt annual output and monitored the details of heat distribution and consumption within the process flow. That was the facility where the crude oil produced from the well undergoes primary treatment – associated gas and water are separated and salts are removed bringing the feedstock to the parameters required for transporting it via a pipeline. It turned out that in its initial configuration the plant consumed circa 178 MW of thermal energy due to combustion of fuel gas in furnaces; and the significant portion of the generated heat is lost. Fuel gases with temperature exceeding 300 °C go directly into the atmosphere, while heated flows of oil and produced water are cooled without returning their thermal potential back into the process.
To optimize this scheme, the researchers used the pinch analysis – the engineering approach allowing for developing the most rational heat-exchange circuit inside the plant. All the key flows were numerically defined indicating temperatures, flow rates and heat capacity. Thus, when marketable oil is cooled from 46 down to 10 °C, it carries over 5 MW of heat capacity, for produced water this indicator is 9 MW, and fuel gases provide for additional 0.18 MW. Simultaneously, the crude oil at the input of the plant needs to be heated almost by 15.4 MW, and air and gas for the burners – circa by 0.9 MW. Overall, the calculations showed that within one plant it is possible to return over 12 MW of heat back into the process.
Based on these data, the scientists determined the key temperature threshold (the pinch-point) and updated the heat exchangers scheme. It was developed to maximize heat transfer from hot flows to the cold ones using furnaces and cooling systems only where internal thermal resources are not insufficient. Eventually, the need for external heat decreased from 178 down to circa 41 MW, i.e., by 77%. In essence, the major portion of heating crude oil and air for combustion is provided for not at the expense of additional combustion of gas, but at the expense of heat which used to be wasted.
A separate focus was on the economics of the upgrade. About 8 km² of heat-exchange surface is required to implement the new scheme, and CAPEX for the new equipment and piping are estimated as USD 4.4 mln. At the time, the annual savings of fuel reaches USD 2.7 mln. Even given the high cost of borrowing, the project will pay back within 3-3.5 years, and the internal rate of return (IRR) exceeds 60%, which is very high for industrial power engineering. The scheme was additionally simplified by refusing from two low-duty heat exchangers of only 1.5 and 3.5 KW. Their contribution into energy saving turned out insignificant, while the cost was comparable with full-featured units. After this engineering simplification, CAPEX went down and the project financials got even better with the energy effect remaining the same.
