Leobersdorfer Maschinenfabrik GmbH & Co.KG (LMF) has developed the trailer-mounted BS 604 compressor unit to facilitate the recovery of natural gas during pipeline repairs.

To safely repair a natural gas pipeline, the respective line section has to be cut off by upstream and downstream interception valves and the contained compressed gas removed from the isolated section. When a major gas pipeline consists of two or more parallel lines, the gas from the isolated section can be transferred to the next section still in service. In the case of a single line, the extracted gas from the isolated section can be compressed downstream the same line. Until now, pipeline operators have often neglected this sound practice and have vented the gas to the atmosphere or to a flare.
Increasing concerns about environmental pollution and the price of gas make this old practice extremely costly and questionable. Even if, for the time being, natural gas venting is still legally possible for safety reasons, operators increasingly are trying to recover as much gas as possible.
In addition to the value of the CO₂ certificates, the value of the gas released to the atmosphere is lost forever. At an approximate value of € 0.25/Nm³ of gas, the gas lost from the pipeline would be worth € 250,000. Due to those environmental and monetary reasons, there is considerable interest to develop and use more sophisticated technologies to reduce methane emissions to an absolute minimum before starting pipeline repair jobs.

The LMF mobile pipeline evacuation unit.

During the transfer of gas before a repair begins, the gas is compressed with gradually reduced suction pressure to a constant discharge pressure of 1015 psi (70 bar) into the operational pipeline or into the downstream section of the evacuated pipeline. This is typical for a reciprocating compressor that is capable of a high compression ratio per stage, and can work under a sliding suction pressure while maintaining a constant delivery pressure within a wide operating range. The operation of the mobile compressor unit has to be completely self-sufficient, which is possible when the compressor is driven by a gas engine fuelled by gas from the closed pipeline section.
In order to guarantee unrestricted operation in all European countries, CE-marking and fulfilment of all relevant European norms and regulations is mandatory.
The complete compression unit, including the tractor, must be designed to comply with European rules to allow the unit to be transported quickly and without the need for special permits.
The new LMF compressor unit is driven by a Caterpillar G3512LE gas engine with a power rating of 1000 hp (750 kW) at a speed of 1400 rpm and a fuel gas consumption of about 8830 cfh (250 Nm³/hr) at full load. The fuel gas feed to the Caterpillar engine driving the compressor is controlled by a gas pressure-regulating station directly connected to the suction side of the compressor unit. There is no need for a separate pipeline-engine gas connection.

LMF compressor BS604
The BS604 compressor unit is minimally lubricated, with four cranks in balanced-opposed design directly coupled to the gas engine. In order to optimize the capacity in conjunction with the high final pressure ratio, the unit is equipped with a patented switch-over between single- and two-stage operation.
The switch-over is performed automatically upon evacuation down to a defined suction pressure without any need for an operator action or mechanical modifications on the compressor package. During single-stage operation, all four cylinders are operated in parallel, whereas in the two-stage operation mode three cylinders perform the first compression stage and the fourth cylinder takes over the second-stage compression.
In the two-stage configuration the compressor is capable of delivering the gas at 1015 psi (70 bar) down to a minimum pipeline pressure of the closed section of
87 psi (6 bar). This allows the recovery of almost 95% of the gas trapped in the pipeline section to be repaired. The remaining 5% has to be evacuated in the conventional way (vent or flare). The base frame is welded in line with WHG requirements in order to avoid leakage of fluids detrimental to the environment. Oil and water are collected in a surge tank mounted inside the trailer frame.
The temperature inside the container is controlled by means of pneumatically actuated flaps and a dedicated fan. The operation with closed container doors reduces noise emission and enables fire suppression inside the container by means of an Inergen fire extinguishing system. The unit is equipped with an automatic fire extinguishing system and nitrogen purging system for the gas lines.

The new LMF Mobile Pipeline Evacuation Unit is an efficient, self-sufficient compressor system, which fulfils the applicable European norms and standards as well as the rules for unrestricted road circulation.