Selecting updated version of compressor station gas cooling system with due regard for equipment life cycle cost

Abstract

An approach is proposed for selecting the most efficient updated (renovated) version of gas cooling system (GCS) based on concordance of energy and economic optimization results. This approach has been put into effect in optimizing the make-up and operation conditions of heat exchanging equipment in the course of its seasonal operation (efficiency criterion−energy cost) as well as in comparing GCS design versions with complete replacement of air cooling devices (ACD) and addition of new ACDs to the existing ones (efficiency criterion−life cycle cost). A general strategy is given for selecting the updated version of GCS of compressor stations (CS), and the characteristics of major Russian-and foreign-made ACDs are compared. An example of solution to problems of compressor stations of gas pipelines (diameter 1420 mm and operating pressure 7.45 MPa) lying under climatic conditions of the central zone of Russia is given.The technical state of the equipment of the gas transporting systems being operated since the 1970s, the change in the gas pipeline operation conditions associated with the depletion of reserves of the existing and development of new fields, and commissioning of new gas transporting systems attest to the fact that it is necessary to update and technically reequip compressor stations (CS) of trunk gas pipelines.Depletion of resources and marked aging and obsolescence of the principal technological equipment (gas pumping units) lead to increased operating costs (excessive consumption of fuel gas, increased frequency, time, and cost of repairs, and maintenance cost) and to reduced operational reliability of the gas pipeline system. In view of this, despite substantial capital investments, the need for complete replacement of gas pumping units (GPU) is indisputable.One of the problems to be solved at the stage of making major technical decisions is selecting unit power and manufacturers of the GPU. As criteria for making this decision, use can be made of net discounted revenue [1] or the discounted cost of the life cycle [2,3]. The second criterion can be taken as optimum for sound and reliable calculation of all components of operational and capital expenditures. In particular, in determining operational costs, attention must be paid to monthly CS operation schedule over a year with due regard for the correctives associated with planned variation in throughput of the gas pipeline [4].

Analysis of efficiency of control of operation conditions of air gas cooling devices at compressor stations

“…Also, while making decision regarding choice of the type of ACD and ACS, it is advisable to use economic criteria, for example the cost of life cycle of the AGCD [6] where K is the capital costs for the equipment, including for realization of the ACS and control of ACD; τ c is the calculated period equal to the recommended investment recovery time for gas industry facilities; C cool + C serv = O ann is the annual operating costs, including the cost C cool for driving the fans and the cost C serv for scheduled servicing of the ACD and equipment control; E is the rate of return [7].…”

“…Based on comparison of AGCDs built around various types of ACD with optimization of the gas cooing temperature t cool [6] for seasonal operation conditions of several CSs, efficiency diagrams were obtained (Fig. 1).…”

“…In terms of combined (total) operating and capital costs over the life cycle of the equipment, the AGCD consisting of an AVG-85MG type of ACD (14 units) has greater advantage over the AGCD consisting of a 2AVG-75S type of ACD (12 units). In spite of a larger requisite number of AVG-85MG type of ACDs, which means higher total cost of AGCD, reduced electrical power consumption by the fans ensures its payback in 5-6 yrs upon diminution of C l.c AGCD by 2-3 % [6].…”

“…The value of this temperature obtained at the stage of optimization of power consumption of the technological section for the assigned CS operation conditions and the average monthly ground temperature [6] are ensured by including an appropriate number of ACD fans in the case of discrete control and by varying the output in the case of speed control. Solution of this problem helps determine, using CS load plots, the annual operating costs for driving the fans successively for each month at the average temperature t a .…”