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Compressor System 

Revamp of a piston compressor system

 

More Flexibility Due to Revamping and Modernization

Once the operating conditions of reciprocating compressors change revamping is a good opportunity to make them fit for current technical specifications and process conditions. Recently NEA modernized recips in an Eastern European refinery to easily meet new requirements. Customers are considering compressor adaptations due to new or extended process requirements. Reciprocating compressors are always tailor-made and designed for a specific operating condition and for long lifetime. New developments and requirements or product specifications demand change operating conditions. Thus, the operators want to modify or revamp their compressors to match the new process conditions or changed capacity as they did in the following case.

In 2003, NEUMAN & ESSER GROUP delivered a reciprocating compressor size 2SZL320H to a refinery in Eastern Europe for a desulfurization process, compressing hydrogen from 28 bar suction pressure up to 85 bar discharge pressure. The reciprocating compressor is a two-crank, horizontal, two-stage, double acting, lubricated service machine with 530 kN max. rod load. The compressor is directly driven by a rigidly coupled electric motor with a nominal driver power of 1,700 kW.

The original design capacity was approx. 33,000 Nm³/h. The NEA scope for the compressor unit as a whole included the pulsation vessels, interstage cooler, interstage separator up to the last stage check valve. After only 5 years of successful operation, the hydrogen gas demand increased approx. 15% due to higher demand on clean fuel.

 

Review of compressor and accessories

 

Verification of Compressor and Accessories Initially, the existing reciprocating compressor is re-calculated according to the original or as-built situation with the NEA compressor design tool KO³ (Compressor Optimization Version 3). This verifies that the compressor fulfills the designated process conditions without deviations and avoids general mechanical or performance problems.

Following this, a calculation is made with new operating conditions. In a first step, a pre-check is made in order to see if an adaptation of the compressor for the new operating conditions is basically possible. The modification of both the compressor itself and the surrounding accessories need to be considered. If the pre-check result is positive, a revamp project is realistic. The second step is the detailed verification of a compressor revamp as an engineering study starting with a thermodynamics and compressor calculation.

For this Eastern European refinery the conclusion was to install a new compressor crankshaft with an increased stroke to fulfill the new requirements within the allowable compressor limits. The piston rods and piston had to be replaced due to the existing cylinders' running length. The advantage here is that the cylinders are not changed; the general compressor arrangement can remain. Using the advanced compressor design tool KO³ several compressor characteristics had to be checked including valve design, mechanical properties and crankshaft strength. Each compressor upgrade also effects a verification of the accessories. The new required compressor performance must be covered.

According to the current legal situation in Europe, it is necessary to comply with the “Machine Directive” (CE) and ATEX regulations, if making significant compressor modifications. Depending on the kind of modification, a revamp and subsequent operation of modified equipment is only allowed in conjunction with a valid original equipment manufacturer (OEM) declaration.

Risk analysis and product safety 

Risk Analysis and Management of Product Safety The NEA GROUP has generated a spark hazard analysis and risk assessment for reciprocating compressor units. If there is a substantial modification, the assessment is performed and measures - if required - are indicated. Just as for new compressor design, major revamp jobs or modifications must comply with the advised product process.

This means use of a procedure for all scheduled quality control instructions, for feasibility study, risk assessment design engineering, and fabrication. A large number of reciprocating compressors run over several decades and many can run even far longer, revamping is a good opportunity to make them fit for current technical specifications and process conditions. With the right technical support by a compressor OEM, the reciprocating compressor can be prepared for long-term operation and match the operating company's demands.

The intensive engineering in advance pays off. This way NEA always provides the technically safest and economically most reasonable solution. This was also the case with the Eastern European refinery. At the end the customer was very satisfied with the result. The delivery took place in time and at the revamp on the construction site was accomplished within only three weeks.