NUMERICAL SIMULATION OF COMPRESSOR STATION AND ADJACENT HIGH PRESSURE GAS PIPELINES ENSURING SURGE FREE OPERATIONS S. Mubin and V.E. Seliznev Department of Civil Engineering, University of Engineering and Technology, Lahore, Pakistan. Corresponding author, email: sajjadmubin@uet.edu.pk Computational Mechanics Technology Center (CMTC), VNIEF-VOLGAGAZ Ltd. Russia ABSTRACT From the point of view of dynamics analysis of high pressure (HP), natural gas pipeline transmission systems from the production sites to the consumers are extremely complicated to simulate numerically, specially through compressor station and flow in adjacent pipelines. A lot of parameters and interdependent variables are involved in the process. The objectives of simulation are primarily safety concerns accompanied with cost reduction in the operation of system. In this paper, natural gas transmission through compressor station and adjacent pipelines is simulated assuming flow as steady state and taking into account surging effects. Keeping in view significant variation in volume and pressure at inlet and out let of CS, simulation is useful to locate the stable working point on the centrifugal superchargers (CFS) performance curve to ensure surge-free operation in gas compressor units (GCU) to simulate different modes of natural gas transmission through pipeline systems (or fragments of pipeline systems). KEY WORDS: Numerical simulation, high pressure natural gas transmission, surging effects, compressor station INTRODUCTION Prime objectives of modeling gas transmission system through compressor station are safety enhancement accompanied by a reduction in the process operational (wear and tear and fuel economy) costs. Operation and maintenance cost of CS include fuel cost and general maintenance of CS which may be significantly high in case of surging and sudden failure. Simulation will not only reduce maintenance cost but also operation cost, in the head of fuels expenses of CS. Russia, the main natural gas exporter in the world spends more than twenty percent of transmitted natural gas as burnt fuel at compressor stations. Therefore, process of natural gas transmission through compressor station and adjacent pipelines needs to be modeled for particular flow characteristics. Special emphasis on surging effect has been made during compression process which significantly damages the CFS casing, impeller blades and even adjacent pipes leading to failure consequences. To understand the compression process of CS a brief description of different components of CS is given below. BRIEF DESCRIPTION OF THE NATURAL GAS TRANSMISSION SYSTEM A typical gas transmission system may comprise of several compressor stations (CS) connected by multi-line parallel laid large diameter gas pipeline segments (GPS). The length of a GPS between two consecutive CS varies from a few dozen to two maximum hundred kilometers. The operating pressure in pipelines generally ranges from 4.5 to 8.0 MPa. GPS can be laid under ground, above ground, above water, under water (at river crossing, offshore pipelines, etc.) or in combination of two or more methods. A compressor station comprises of one or several gas compressor shops (CSh). A group of GCU operates within a compressor shop (Fig. 1). GCUs are connected in gas compressor shops with high pressure interconnected single-loop gas pipelines (CGP). The length, generally, does not exceed from two thousand meters. The natural gas before supplying to compressor units is passed through separating filters and/or dust catchers to clean liquid and solid impurities. GCUs are subdivided into reciprocating and centrifugal units depending on their operating principles. Reciprocating GCUs have low capacity and are mainly applied for a low flow rate (Atavin, et al., 2000). In this study, gas compressor units are considered with CFS (Fig. 2). Such gas compressor units are conventionally divided into two interdependent components: a) CFS and b) electrically derived motor or gas turbine unit, capacity of which varies from 4 MW to 27 MW depending on the GCU type. The power is derived to CFS via coupling. A gas compressor station is usually equipped with multi-type GCUs. However, in reality even when a CS is equipped with just one type of GCUs, the actual performance differs depending upon their maintenance and degree of wear and tear. To ensure the safety of the GPS, the transmitted gas is cooled in air in cooling devices (ACD) to a temperature of 308 o K. In the 1