The intent of this work is to propose a simple alternative to estimate the fuel consumption in the compressions stations making use of the available data at pipeline control room. The basic idea is to take advantage of the correlation that exists for fuel flow rate to air inlet temperature and axial compressor speed of the turbine. This approach is applied in two-shaft gas turbines where the gas producer turbine is not mechanically coupled with the part load turbine, which permits the turbine operates under the characteristic of a unique running line. The correlation is modeled by mean of linear functions with the coefficients adjusted using an ordinary least square for each turbine unit. The operational data is acquired, processed to remove noise and low quality values and regressed to obtain the linear coefficients. To verify the proposed model, the fuel flow is calculated and compared with data provided by flow meters. This comprises an operational window of seven consecutive days where is shown the total fuel consumed per day of all unit in operation and the total consumed per unit during the seven days. Additionally, to analyze the behavior of the model in transient conditions is presented a comparison and the difference between measured and estimated is plotted for the time window. The first comparison reveals an error lower than 5% per day, while the error accumulated per unit is lower than 8%. However in the transient analysis larger differences are noted mainly during abrupt changes in the turbine speed. As a general remark the model could also be used in the identification of fuel metering failure and prevent the spurious measurement data being considered.
The Bolivia-Brazil pipeline (Gasbol) was designed to transport up to 1.1 billion cubic feet (31 million cubic meters) per day of natural gas. Part of the gas flowing through the pipeline is necessary to conduct its operation. A small part is used as source of energy to feed the city gates‘ heaters while a significant amount of gas is necessary to operate the compression stations by mean of heaters, generators and engines to drive the compressors. When the pipeline is operating at maximum transport capacity the pressure loss is increased due to friction and consequentially the fuel consumption. In this scenario, the volume of gas necessary to operate the compression stations may reach up to 5% of the total volume transported. Figure 1 gives an overview of the fuel usage grouped per equipment consumption representing a typical operational profile. The compressor engines are responsible for 93% of the total energy consumed that is significantly higher than the other equipment. This volume of gas extracted from the system should be correctly computed due to a lot of motives. Given that TBG is not the owner of the gas transported it is extremely necessary to reduce the uncertainties regarding the measurement chain. Moreover, at the end of the operative day, it is highly desirable to close the mass balance equation on the Gasbol.
