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- 1. ValveReport To: XXX of XXX From: Leonard Lin, P.Eng. Fax: XXX Pages: 11 Phone: XXX Date: Tuesday, May 23, 2006 Re: W76 2nd stage CC: X Urgent X For Review ( Please Comment ( Please Reply ( Please Recycle The purpose of this report is to find the reason of present valve failure in 2nd stage and propose a solution by using smaller cylinders. 1. Input Data The compressor is COOPER W76. The present valves are 4” modified 90CT, version M4, in 2nd stage. The simulation used 2nd stage pressure at 694 psig (4,785 KPA) suction pressure with present 5.750 bores, 776 psig (5,351 kpa) with the proposed 4.250 bores and 2,506 psig (17,282 KPA) discharge pressures. The unit is operating at the fully loaded condition (all cylinders are double acting) and at 900 rpm, The compressing gas is 98% of Ethane with 1.043 SG, which has the critical point or Cricondentherm at 4,789 kpa and 35 dgC. 2. History and observations: Sample
- 2. February 6, 2016 These 2 W76’s have the valve problems for a long time. The OEM valves were reported to fail every 3 weeks and they been modified many times since 1993. Please refer the following engineering report: 1993 the two new units were in the service March 1994 OEM Cooper made the report. April 1995 Beta Machinery made the valve report August 2002 Klaus Enterprises report and designed new type of plate valves with thermoplastic plates. The 1st stage valves lasted 3 years since installed in 2002. It was reported a major horsepower saving with these new valves. Dow and Klaus worked together and made 5 times (M0-M4 versions) modifications on the 2nd stage valves but these valves keep failing every 4-6 weeks. It should be noted that the present 2nd stage suction condition (4,785 kpa, 40dgC) is very close to the critical point. We found more suction valves failed than the discharge valves although there was a much higher impact and pressure drop in the discharge. 3. Valve Performance Simulation indicates that the present valves in 2ND stage suffered from high impact 310 in/s, high pressure drops and high Q values, which are significantly above our guideline and cause these valves to break quickly. In order to solve the problem, we suggest modify 5.750” bore into 4.250” with the same 2nd stage valves installed. The following valve data for comparison: Page 2
- 3. February 6, 2016 2nd cylinders OEM 5.750 bore 4.250 cylinder Suction Discharge Suction Discharge Valve type 90M4 90M5 Plate material 7 mm Nylon 7 mm Nylon 7 mm Nylon 7 mm Nylon Cushion (mm) 1 2 1 2 Lift (in) .090 .060 .090 .060 Guide ring (in) .444 .462 .444 .462 Springs (lb x no) 27# X18 KCS-1711 50# X18 KCS-1613 27# X18 KCS-1711 50# X18 KCS-2214 Buttons BT-10-7 230029FR365 BT-10-7 NO Max impact (in/s) <300 242 310* 220 285 API valve velocity (ft/min) <7,000 8377* 12,566* 4,577 6,865 Max. P drop (%) <10 17.08* 18.66* 7.56 8.73 Valve loss (%) <8 7.45 9.56* 3.80 5.46 Pseudo Q 1<Q<15 19.62* 33.99* 7.81 13.52 Table 1 Valve setup and performance in 2nd stage HE cylinder Note: • * = Out of valve reliable area • All predicted data from head end cylinders for the max values Page 3
- 4. February 6, 2016 4. Compressor Performance COOPER Performance program was used to predict the compressor performance. The flowing table lists the comparison at the fully load condition: W76 #83-5.750-2500 present cylinders #608-4.250-4500 New cylinders Modified 5.75” into 4.25” bore Flow (kg/s) 14.97 13.39 13.23 TOT Required HP 4,102 3,090 3045 2nd Suction P (kpa) 4,785 5,350 5,406 Max Td (dgC) 1st @Ts1=28 2nd @Ts2=40 85 125 91 107 92 107 Max rod load (lb) 1st 2nd 56,227 63,002 62,903 31,211 63,636 31,145 Compression ratio 1st 2nd 2.597 3.672 2.898 3.290 2.928 3.257 2nd stage cylinder clearance (%) HE CE 17.0 18.2 28.2 28.3 36 47 Ref file Cascad1 Cascad2 Cascad3 Table 2 Compressor performance at full load condition Note: The cylinder clearance used in the calculation is base on Cooper existing cylinder data. The actual clearance for the modified cylinder can be calculated: Assume max 4" hole on the cylinder liner for valve pocket holes, Clearance per valve hole = 4x4xpi/4 x0.75 = 9.42 cu in or Total add clearance = 9.42 x2 (no of valves per end) = 18.85 cu in per cylinder end This will add: 19 % clearance for 4.25HE and 29% for 4.25CE. The total clearance from 5.75 cylinder to 4.25 cylinder will be: 4.25HE=17+19=36% and 4.25CE = 18+29=47% Page 4
- 5. February 6, 2016 5. Conclusion 2nd stage valve failure was mainly caused by the large cylinder with a small valve flow area in this Ethane gas application. A further increasing valve flow area was limited by the diameter of OEM valve pocket. It was proved by the report that reducing 2nd stage cylinder bore size will solve this problem. Simulation shows that valve life will be significantly improved if the cylinder was changed from 5.750” to 4.250”. From Table 1, we can expect a good valve performance and a normal valve life in 2nd stage. The benefits to modify the existing 5.750 cylinders into 4.250” also include: a. Huge cost saving on preventing from purchasing the six new cylinders and the new valves b. 2nd stage suction P will increase 621 kpa, and this will move the gas condition away from the critical point and prevent the liquid into suction valves. Table 2 shows that the compressor capacity will reduce from 14.97 to 13.23 kg/s or 11% and the required HP will reduce by 1,057 hp or 26% after the modified cylinders installed. Enclosed please find the COOPER results in the 3 cases shown in Table 2. The simulation results about 10 pages will be sent on request. Page 5
- 6. February 6, 2016 5. Conclusion 2nd stage valve failure was mainly caused by the large cylinder with a small valve flow area in this Ethane gas application. A further increasing valve flow area was limited by the diameter of OEM valve pocket. It was proved by the report that reducing 2nd stage cylinder bore size will solve this problem. Simulation shows that valve life will be significantly improved if the cylinder was changed from 5.750” to 4.250”. From Table 1, we can expect a good valve performance and a normal valve life in 2nd stage. The benefits to modify the existing 5.750 cylinders into 4.250” also include: a. Huge cost saving on preventing from purchasing the six new cylinders and the new valves b. 2nd stage suction P will increase 621 kpa, and this will move the gas condition away from the critical point and prevent the liquid into suction valves. Table 2 shows that the compressor capacity will reduce from 14.97 to 13.23 kg/s or 11% and the required HP will reduce by 1,057 hp or 26% after the modified cylinders installed. Enclosed please find the COOPER results in the 3 cases shown in Table 2. The simulation results about 10 pages will be sent on request. Page 5