How to Optimize Cylinder Valves Design (Print)
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How to Optimize Cylinder Valves Design If diagnostic and service improve reciprocating compressors availability, a clever design with an appropriate ratio among new technologies can enhance the mechanical behaviour for a better reliability
Fig.1.: Compressor valve.
Authors !nzo "iacomelli, Consultant !ngineer, and Claudio Vaglini, Customer #upport !ngineer Reciprocating compressors are used in many services for Oil & Gas, with special process requirements. The range of capacities, operating conditions and molecular weights make the use of such machines very flexile. There is a continuing focus to improve operation, maintenance and consequently the availaility of the plants that implies guidelines and precautions to e considered since the fi rst design of the machines. That is important for the cylinders valves !"ig.#$ as they are one of the most critical part in a compressor compressor..
$argeting Valves %eliability The proper selection of technologies and design procedures helps for an optimi%ation of mechanical ehaviour, a minimum energy consumption, in compliance with the specifications, to cover the requirements. n refinery, chemical, petrochemical, natural gas and other industrial plants the operating conditions are different as a function of the applications. The pressures can reach '()*pa for +- production and molecular weights are very variale. Reciprocating compressors cylinders are luricated ut dry applications are also required to avoid pollution of the product. The presence of dirt and liquids entrained y gas influences the actual operation. n refinery /0 production process have different degrees of cleanliness. "or heavy duty services it is necessary a wide capacity control of the compressor to adapt the operating conditions according to process requirements. The valve can e of different types like disk, ring type, poppet, with flat surface or special profiles. *etallic shutters have een replaced y plastic components, apart of low temperatures or very high pressures, due to the great adaptaility to non controllale conditions !dirty or liquid presence$. The materials of the valves for heavy duty applications in Oil & Gas are su1ect to requirements 2- 3#4, additional specifications of ngineering 5ompanies and end users.
Design &odeling and #imulation 6alves design related to mechanical and f luid7dynamic aspects, affecting the reliaility of the machines, needs advanced methods, simulations, technologies, high material quality. *athematical models are ale to descrie the pressure drop through the valves and the plate motion in operation. The shutters are su1ected to the forces due to spring, fluid drag, inertia and damping. *any parameters are involved and the main i nput data are cylinder geometry, properties of gas !*olecular weight, 5p85v ratio$, R-*, suction, discharge temperature and pressure. The outputs are plate movement, compression cycle, power loss at the valve, total power asored y the compressor, pressure pulsations in plenum chamers, no%%les, dampeners and piping.
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How to Optimize Cylinder Valves Design (Print)
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The lift is calculated for an adequate gas velocity, with consequent evaluation of pressure drop and spring load, to compromise between energy saving and valve mechanical behaviour. Excessive fluttering may cause a reduction of the li fe of springs, with consequent problems to the plates. For refinery applications, the gas velocity is normally higher due to the small lift required, as the drag force on the rings is low due to the low MW of the gas. The life of the valves is greatly influenced by the movement of plate that should reach the guard and eep the position till the closure starts, with the condition to occur before the dead point. !uring the opening period the fluttering should be minimised to reduce the fatigue effect on the springs and multiple shoc against the seat. The valves are to withstand the operating conditions, environmental and dynamic aspects, considering the corrosion, particularly for rings and springs, undergoing fatigue stresses. FEM "Finite Elements Method# is used for strength determination of bodies, plates and for the natural frequency analysis "Fig.$#. The fluid%dynamic aspects are investigated with &F! "&omputeri'ed Fluid !ynamics# to optimi'e the development of standard series of valves.
&onitoring and Diagnostics The instruments to control process parameters, such as temperature and pressure in suction and discharge help to evidence abnormalities. (n addition the temperature of the cover surface can be measured to verify the correct performance of the valves. Monitoring and !iagnostics systems anticipate problems and eliminate most of the riss. Failures affect operation and safety of personnel. (n addition, they determine equipment damages and production losses. (n a multistage compressor the inter%stage pressure variations are a further help to give an identification of the origin of the problems. The control of valve performance is made with the analysis of thermodynamic parameters, with acoustic emission analysis and in more detailed way by measuring the compression cycle and the pressure upstream and downstream the valves. )uitable instrumentation can be used for spot analysis or continuously with on %line monitoring. The malfunction of the valves can be predicted and the most suitable period selected for replacement, possibly combined with other maintenance activities, thus reducing the ris of shutdown of the plant and increasing the availability.
&aintenance and #ervice The strategies of *reventive, *redictive or *roactive Maintenance depend on the type of machines, criticality of the service and on the possibility to count on +condition monitoring+ or +diagnostic systems+. Machines and valves should restore the original performance "MTF# and eep the ti me for maintenance at the minimum, as directly affecting the availability of plants. Therefore to reduce the MTT- is necessary to / replace immediately a valve with a spare / combine these interventions with other possible needs to stop the machine / plan the activities with a general shut%down 0alves can run smoothly with very good results, by reaching operating life of about 1 years or more depending on the applications. The presence of dirt, liquid or other things in the gas are worsening the operation.
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How to Optimize Cylinder Valves Design (Print)
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Experts of valves and compressors give Engineering Support, Reconditioning and Upgrades and a more prompt solution to the ongoing operation deviations. High Quality valves are necessary to reach good performance and a longer MT! "Mean Time et#een !ailure$, #ith conse%uent reduction of maintenance interventions in heavy duty applications. The valves are reconditioned &y replacing the internal parts "rings and springs$, &y the #or'shop of the pl ant or &y external service shops. The reconditioning has to &e carried out &y %ualified personnel, respecting strict repair and reconditioning procedures to have valve components of excellent %uality and as ne#. R() can improve valve life, reducing maintenance costs and increasing the availa&ility in case of dirty gas. Special plastic plugs avoid the relative movement &et#een metallic parts "!ig.*$, avoiding #ear of counter+seats and springs.
Dott. Ing. Mario Cozzani Srl
PCN Europe Magazine u&lished since -/, 01 Europe has &ecome a reference pu&lication in Europe covering the latest industry ne#s, application stories and product ne#s from and for the processing #orld, including the chemical and pharmaceutical, food and &everage, oil and gas, as #ell as the ru&&er and the plastic industry. 2t is the indispensa&le source of information for processing professionals to get an update on #hat is happening in their industry. 3ll rights reserved 4 -56 + T2M7lo&al Media 0ontact us + !ollo# T2M7lo&al Media on 8in'ed2n for c ompany updates
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