Often, reciprocating compressors are used to handle very dirty and corrosive gases that have a negative Impact on the life of their components and can affect plant productivity. In such cases, installation of a condition monitoring system that enables operating the compressor safely by warning the operator in advance that maintenance is necessary, will increase the whole plant efficiency. This is why Petrobras (Petróleo Brasileiro S.A.) asked PROGNOST Systems to install its PROGNOST®-NT system on two Mannesmann Demag reciprocating compressors.
The compressor duty is to compress the excess gas derived from pyrolysis extraction from shale. The plant is equipped with two Mannesmann Demag compressors, C-24101 A/B type 23B4G3/17. These are four-throw, balanced-opposed, reciprocating compressors with lubricated cylinders. The compressors are driven by 1408 hp (1050 kW) electric Motors at a speed of 504 rpm. The shale gas (hydrogen sulfide) is compressed in three stages. Between stages, extraction lines take out several condensates: fuel gas, a small percentage of naphtha, gas Treatment with soda and DEA (H2S extraction) and, at the end of the third stage, the LPG at about 230 psi (1550 kPa). The compressor service is very demanding because the shale gas has high humidity and entrains any solid particles in suspension that are the cause of the majority of the Problems and accidents with these machines.
The main problems are caused by the deterioration of the sealing elements (packing leakages) and consequent H2S attack on the internal compressor parts. These leakages led to possible condensate ingestion, and probable frequent condensate fog ingestion, as well as capacity loss because of valve obstruction. A few years after the installation of the machines, Mannesmann Demag stopped manufacturing reciprocating compressors, and Petrosix had no help to solve the problems. More recently, Neuman & Esser bought the rights to service Demag compressors and the German company made some recommendations, such as implementing temperature control of the cooling water, use of nitrogen as packing buffer gas, improvement of gas treatment to lower the amount of condensate and solid entrainment. These reciprocating compressors, however, did not have any devices allowing either predictive maintenance or early failure warning of the running parts.
In 2005, Prognost presented ist Prognost-NT monitoring system expressly tailored for reciprocating compressor diagnostics. At São Mateus do Sul, the equipment operators had no experience in monitoring this type of machine. They only had a Monitoring system installed on an old 9.4 hp (7MW) Sulzer axial compressor installed in 1984, which allowed them to perform predictive maintenance. Prognost specialists were able to explain to Lampert and Chaves the differences between a monitoring system installed on turbomachinery and one designed for reciprocating machines. They stressed the importance of continuously monitoring the machine and process conditions. This activity helped the machine failure diagnosis and/or operation out of the machine operating limits, giving support to the decision to intervene, leading and helping the problem analysis and, mainly providing machinery protection. In the next step, Prognost formulated the specific monitoring objectives for the client. Finally, the whole system was purchased by Petrobras.