Filtration System Designed To Improve Gas and Engine Oil Life
(Reprinted from October 1994 Diesel & Gas Turbine Worldwide)
 In their ongoing efforts to obtain more fuel-efficient operation from their machines, engine builders and
operators have had to address the agonizing issue of short lubrication oil life. While still a major concern, new filtration systems are making short work of the problem today.
Unacceptably short lube oil life has been a chronic problem generally associated with lean-burn, gaseous-fueled engines. When increasing the air-to-gas ratio in order to obtain more fuel-efficient
operation, oxidation and nitration of the lube oil can become a major problem in terms of engine longevity, manpower time and general overall maintenance costs.
Oxidation, according to oil analysis companies, is a leading cause for lube oil degradation, which translates into the need for more frequent oil changes. Oxidation products are formed by the
decomposition of the oil at high temperatures in the presence of oxygen. Among the products that can be formed during this process are aldehydes, ketones, alcohols, carboxylic acids, anhydrides
esters, ethers, as well as organo-nitrates and nitrate esters. These compounds, and others they may form, commonly come under the label of sludge and occur in most internal combustion engines.
As these compounds build up, oil viscosity increases, causing an increase in pressure drop across the
filter. This in turn shortens oil and filter life. In addition, the lubricating ability of the oil itself is
reduced as these compounds react with the additive packages, either through general depletion or precipitation.
Further negative consequences occur if the oil is not changed. One such consequence occurs when a filter bypass valve opens because of the increased pressure drop, which allows unfiltered oil to
circulate. In engines without internal bypass valves, the high-pressure drop eventually causes low oil pressure, which stops the engine.
While oxidation is common to all fuels, nitration is primarily a problem in natural gas-fired engines. Nitration products occur when NOx (formed during combustion), reacts with oil to form
organo-nitrates and nitrate esters. These thicken the oil and cause lacquer and varnish formation.
The problem intensified by lean-burn setting that burn more air, thereby increasing the amount of nitrogen present and creating more harmful nitration products.
Although these problems have been plaguing engine builders and operators for decades, there are two possible solutions to them: enlarge the sump capacity of the lube oil system to delay the viscosity
increase; or improve the filtration system to remove both the fine particles which catalyze oxidation and nitration reactions and sludge.
In 1983, a combination of the two solutions was developed in one filtration system. Since that time, it
has been tested thoroughly in general field conditions as well as in specific test sites developed by a major engine company. The unusual system consists of a relatively large filter housing containing
either 7, 14, or 21 ram packed depth-type elements. The housing provides additional sump capacity.
The highly absorbent media removes the oxidation and nitration by-products and acidic moisture that cannot be removed by conventional barrier filters or centrifugal oil filters.
The system was first installed over ten years ago on a Caterpillar 399TA gas-fueled engine in Kellyville, Oklahoma, U.S.A. An operator, Union Pacific Resources, was chosen for the test because of
an initial contact with Hawkins Filtration, a representative in Tulsa, Oklahoma, concerning the quite short, 720-hour oil and filter change intervals and the frequency of major overhauls. After
implementation of the new filter system, the oil drain period was extended to 2000 operating hours and the Kellyville engine ran without overhaul for well over 70,000 hours.
This initial field test resulted in three primary benefits being recognized by the engine operator. First,
the operator found that the new system reduced oil and filter usage by 75%. It also reduced engine
downtime. And it significantly reduced man-hours spent on engine maintenance. After analyzing these filter system had paid for itself in less than one year.
In 1986, a more extensive field test was conducted jointly at a cryogenic gas complex operated by Union Pacific resources near Carthage, Texas, by Nelson/Winslow, Western Filter Co. Inc., Hawkins
Filtration and a major engine manufacturer. The test spanned two six-month periods and now continues as standard procedure on all similar engines for that operator. The maintenance technician,
Robert White said the filtration system, " has been very beneficial in reducing maintenance costs, downtime and improving the company's ability to be a low cost provider."
This trial was evaluated with an oil analysis program that monitored TAN, TBN, oxidation and nitration levels, as well as wear metal contaminants. Although this is more expensive than traditional
oil analysis, chemical changes in the oil must be monitored to determine safe oil drain periods. While
conventional full-flow filters are adequate for wear particle control, the addition of a proven absorptive
auxiliary oil filter is necessary for the control of chemical contaminants in the oil. The results here, as
well as at other sites, are caused by the effective control of chemical contamination, which can account for as much as 40% of total engine wear. According to company data, oil drain periods can be
extended two to three times by instituting this filtration technique.
Since that first test over a decade ago, other operators of various engines who have installed the
system have reported improvements in their oil analysis and engine performance. Some engine operators have now requested that packagers provide this system in their quotations for new engine equipment.
In the mid-1980s, the time saving factor of the new filter system became increasingly important as major oil companies found it necessary to cut personnel. Today, however, the system not only
creates reduced down time periods, but also helps firms reduce solid waste disposal costs, which have been on the increase because of new environmental regulations passed by the federal government.
Companies that have taken advantage of these benefits include: Texaco, Delhi Gas Pipeline, Union Texas Petroleum, Phillips Petroleum, Union Pacific Resources, Kerr McGee, HCA Hospital, Total
Compression, Hanover Compression, Compressor Systems and others. Each of these companies have proceeded with retrofitting their entire fleets with the unique filter system.
Today this lube oil system, (now manufactured and distributed under the Nelson/Winslow brand
name), is available in both full-flow for retrofit or in bypass for auxiliary filtration. It is also available as
standard or optional equipment on some natural gas engines produced in the United States. Because of the ten years of successful experience with this system, the manufacturer offers guaranteed
performance contracts on these auxiliary oil filter systems.
With engine operators and their respective companies demanding more and more efficiency from their
engines, the Nelson/Winslow line of filtration systems are a welcome addition to any natural gas-powered engine room. |
