Lubricating system

For combined cycle turbines Single lubrication system Low pour point Extreme pressure and anti-wear properties Hydrolysis stability Water separation... 

The viscosity of a hydrocarbon mixture, as with all liquids, decreases when the temperature increases. The way in which lubricant viscosities vary with temperature is quite complex and, in fact, charts proposed by ASTM D 341 or by Groff (1961) (Figure 6.1) are used that provide a method to find the viscosity index for any lubricant system. Remember that a high viscosity index corresponds to small variation of viscosity between the low and high... 

A considerable number of experimental extensions have been developed in recent years. Luckliam et al [5] and Dan [ ] review examples of dynamic measurements in the SFA. Studying the visco-elastic response of surfactant films [ ] or adsorbed polymers [7, 9] promises to yield new insights into molecular mechanisms of frictional energy loss in boundary-lubricated systems [28, 70]. 

The often-cited Amontons law [101. 102] describes friction in tenns of a friction coefiBcient, which is, a priori, a material constant, independent of contact area or dynamic parameters, such as sliding velocity, temperature or load. We know today that all of these parameters can have a significant influence on the magnitude of the measured friction force, especially in thin-film and boundary-lubricated systems. 

Foam Inhibitors. Methyl sihcone polymers of 300-1000 mm /s(= cSt)) at 40°C are effective additives at only 3—150 ppm for defoaming oils in internal combustion engines, turbines, gears, and aircraft appHcations. Without these additives, severe churning and mixing of oil with air may sometimes cause foam to overflow from the lubrication system or interfere with normal oil circulation. Because sihcone oil is not completely soluble in oil, it forms a dispersion of minute droplets of low surface tension that aid in breaking foam bubbles. 

Opening the suc tion valves by some external force (oil from the lubricating system, discharge gas, electromagnets. . . ). 

The lubrication system, for reliabihty reasons, usually has an operating and a standby pump and dual switchable filters. If there is a cooling-water scahng problem, coolers may also be switchable. 

Lubrication is typically provided by two separate oil pumps—a direct shaft-driven pump on the gear case and an auxiliary electric motor-driven oil pump that is usually mounted on a lube skid or similar sub-base. Oil filters, oil coolers, and oil heaters complete tlie lubrication system, which has many (if not all) feamres in coimuon with traditional auxiliary systems. A typical schematic is shown in Figure 4-42. 

In many cases, the most frequent cause of equipment outage is the lubrication system. Because magnetic bearings do not wear out, and do eliminate oil, pumps, filters, coolers, and regulating and mixing valves, the potential for improved reliability is obvious. Reliability is also enhanced by the control system, which offers continuous real-time protection. The system automatically shuts down before machinery damage can occur. 

This standard could be adapted to the fuel compressor for the natural gas to be brought up to the injection pressure required for the gas turbine. Covers the minimum requirements for reciprocating compressors and their drivers used in petroleum, chemical, and gas industry services for handling process air or gas with either lubricated or nonlubricated cylinders. Compressors covered by this standard are of moderate-to-low speed and in critical services. The nonlubricated cylinder types of compressors are used for injecting fuel in gas turbines at the high pressure needed. Also covered are related lubricating systems, controls, instrumentation, intercoolers, after-coolers, pulsation suppression devices, and other auxiliary equipment. 

The lubrication system for the turbine is designed to provide both lubrication and cooling. It is not unusual that in the case of many gas turbines the maximum temperatures reached in the bearing section is about 10-15 minutes after the unit has been shutdown. This means that the lubrication system should continue to operate for a minimum of 20 minutes after the turbine has been shutdown. This system closely follows the outline in API Standard 614, which is discussed in detail in Chapter 15. Separate lubrication systems for various sections of the turbine and driven equipment may be supplied. Many vendors and some manufacturers provide two separate lubrication systems One for hot bearings in the gas turbines and another for the cool bearings of the driven compressor. These and other lubrication systems should be detailed in the specifications. 

For gas turbines, especially the more advanced high-temperature gas turbines, the oil of choice should be synthetic oil, since synthetic oils have a high flash point. Gas turbine lubrication systems should be run for about 20 minutes after shutdown since maximum temperatures are reached after 10 minutes of shutdown especially in the bearing area. Most gas turbines are also on turning gear to avoid sagging in the shaft. Mineral oils can be used for the compressor. It is not uncommon to have two types of oil in a petrochemical plant. Mineral oil costs much less than the synthetic oil. 

Lockup-worn and broken teeth Contaminated lubrication system, excessive misalignment... 

The gas turbine is a complex system. A typical control system with hierarchic levels of automation is shown in Figure 19-3. The control system at the plant level consists of a D-CS system, which in many new installations is connected to a condition monitoring system and an optimization system. The D-CS system is what is considered to be a plant level system and is connected to the three machine level systems. It can, in some cases, also be connected to functional level systems such as lubrication systems and fuel handling systems. In those cases, it would give a signal of readiness from those systems to the machine level systems. The condition monitoring system... 

Lubrication skid. The gas turbine lubrication skid is usually independent of the steam turbine skid as the lubrication oil is usually synthetic due to the high temperatures in the gas turbine. Another reason is due to water contamination of the lubrication oil from the steam turbine. It is advisable to have the lubrication system be totally independent. The gas turbine lubrication skid would report to the gas turbine controller. Since the lubrication system is also used for providing cooling, it is usually operated for about 20 minutes after the gas turbine is shutdown. The lubrication skid contains at least three pumps, two pumps in which each can provide the head required and a third pump, which is usually recommended to be a DC drive for emergency use. These pumps and their control fall under the drive level hierarchy. 

Clean-out of the lubrication system, including chemical cleaning and passivation, where required. 

The pressurized lubrication system is a more elaborate lubrication method (.see Figure 3-19). The system has a main oil pump, either crankshaft or separately driven, a pump suction strainer, a cooler when needed, a... 

Lubricated cylinders use a separate mechanical lubricator to force feed, in metered droplet form, a very precise amount of lubricant to specified points. This minimizes the amount of lubricant in the cylinder and allows a lubricant most compatible with the gas to be selected without compromising the frame lubrication system. Lubricant is fed to a point or points on the cylinder to service the piston rings and the packing when required. In a few cases, as in air compressors, the packing is lubricated from the crankcase. On some applications involving wet CO7 or H2S m the gas stream, special materials may be avoided if one of the lubrication points IS connected to the suction pulsation dampener. 

Lubrication is splash type and grease is used on the more competitive models. There are variations available with internal pressure lubrication systems. Some models can be equipped with an external lube system, and for rare cases, API 614 lubrication systems have been proposed. 

As with many consumer goods, compressors cannot be purchased without accessories. Some of the accessories are essential to the basic operation of the compressor, such as lubrication systems and couplings. Other accessories, such as the anti-surge control equipment, are optional in order to enhance operation but are not essential. The accessories may be purchased from the equipment vendor or they may be purchased from another party—a decision open to the purchaser. Generally, the accessories essential to the operation are purchased from the equipment vendor as part of the original purchase. The lubrication system and couplings are classic examples of this option. Intercoolers, while essential, are not normally purchased from the equipment vendor if the application is a process compressor. 

This chapter will cover some of the more common accessory items for compressors such as the lubrication system, gears, coupling, instrumentation, vibration monitoring, and process control. The subject is broad and far-reaching. It is hoped that, for the first-time user, this discussion will be a good introduction and, for the veteran, it may offer another perspective on the subject. 

Chapter 3, which discussed various reciprocating compressors, stated that riiaii> reciprocators use a pressure-fed lubrication system for the frame bearings. This system is built into the crankcase in many applica tions. I he basics of these systems follow the fundamental criteria which will lie discussed with the fully separate system. The larger reciprocating compressors may use a separate frame lubrication system. 

Figure 8-3. Lubrication system for a compressor that requires two levels of pressure.

In many ways the pump is the heart of the lubrication system as it is the only active element. It must furnish sufficient capacity at a high... 

One problem with the vendor test stands is that they fall into the do as 1 say, not as I do category. This means the test stand lubrication system bears little resemblance to the nice API 614 lube system purchased with the compressor. The user should not be surprised if he finds the vendor s test stand lube system to be somewhat on the shabby side, depending, of course, on the age of the test stand. 

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