Filtration improves efficiency of heat transfer systems and triples life of pumps.

Implementation of a hot oil filtration system has resulted in improving the efficiency of heat transfer systems leading to reduced downtime and costs for a die casting company, while tripling the life of its heat pumps.

Faced with the inherent problems of using heat transfer fluids for process heating, Twin City Die Casting decided to switch to a simple but extremely effective solution to its heat transfer system problems when it implemented Liquid Process Systems' filter to continuously filter the oil while operating their systems.

Need for hot oil filtration

Many die casting companies and other industries use hot oil heat transfer systems for heating dies in the manufacturing process. The Twin City Die Casting plant uses 13 heating systems for starting up and keeping dies hot. Each process has its own individual electric heating unit which is portable and includes its own heater, reservoir, pump, controls and so on for providing hot oil to the process continuously.

Heat transfer fluid is circulated between the heater and the dies to provide consistent, uniform heating for manufacturing of parts, but over time the oils and systems fall victim to natural processes of oxidation and general wear, creating such contaminants as coke and sludge, and causing fouling of heater element surfaces and oil passageways in dies.

The hydrocarbon oil used in these systems eventually breaks up over time, producing carbon that turns the oil black. In time, concentrations of carbon turn to coke, residue from the used oil, and sludge. These fine particles (if not filtered) quickly build up and coat the heat transfer surfaces and foul the dies, heater elements, pump internals and seal faces.

These particles also cemented on to the heater elements and any low flow areas of the circulation loop. Coke and sludge made the operation of the relief valve sluggish and sometimes the poppet spool would get stuck.

All of these impediments caused by coke and sludge broken down from the unfiltered oil were said to make the work of producing components more costly and inefficient. This is the reason the company sought hot oil filtration.

System detailed

Since their installation in late 1996, the pumps are said to be lasting on average three times longer. The end result of installing the filters was said to be less frequent repairing of pumps, which meant an overall cost savings in labor and downtime.

The cost of pump repair and labor was estimated at $700 per pump per breakdown, but now the filters are said to have increased pump life by three times its normal life. Currently, Twin City Die Casting has 13 heating units. Each of these units has been equipped with its own filter.

Operating at temperatures up to 500 [degrees] F (260 [degrees] C), the filters are said to clean and maintain efficiency of heat transfer fluid and oil, continuously clean the fluid without disrupting system operation, reduce wear of such rotating assemblies as pump rotors, impellers, seals, valves and stems, increase the life of the heating system and reduce downtime. Cost due to fluid degradation has been reduced, wear of dynamic seals is optimized, and burnout or cracking of the heater surface has also been minimized.

Other results

When implementing the filters at Twin City Die Casting, the differences between the used oil that was filtered and the oil that was unfiltered were noticeably different, even to the naked eye (figure 1). The unfiltered oil had more coke. The filter had improved the oil's viscosity, which is characteristic of fluid flow per unit time that indicates thermal degradation. The improved viscosity and reduced particle count indicate that oxidation has been reduced and the oil's life will last longer.

[Figure 1 ILLUSTRATION OMITTED]

The oil's life is said to have increased and the oil has not deteriorated as much as it did before filtration. Estimation or quantification of the amount of oil saved or how much the life had increased were impossible, since these systems are constantly opened in normal operation. When these lines are disconnected, oil is constantly replenished, and it is thus difficult to make estimations or projections on the oil's life.

To put it in perspective, replacement costs for a 55 gallon drum of heat transfer fluid range anywhere from $400 to $800, according to Liquid Process Systems. Add to this maintenance man-hours, repair time and the cost of replacement parts such as seals, valves, rotors, volutes, mag-drive canisters and the like, and costs are said to quickly become considerable.

The pumps themselves still eventually need replacing, but now need to be replaced less often due to filtering. Cost of a typical pump can be estimated at about $1,200.

The cost of each filter paid for itself within the first few weeks of installation and implementation. These filters and systems are said to normally pay for themselves within the first six months of installation, or in most cases sooner, by eliminating the regular maintenance costs that were previously required.

It was also found that the amount of sludge that accumulated in the system's heating chambers was reduced and that the relief valves did not gum up or stick. Improved operation of these relief valves, especially in heat transfer systems, is an increased safety benefit, due to the potentially dangerous high temperatures and pressures involved with these systems.

Filtration explained

A traditional method for filtration of hot oils has been to incorporate a strainer before the system pump. Strainers are designed to protect a piece of equipment, such as a pump, valve or flow meter. The strainer must be cleaned regularly to prevent cavitation, which causes mechanical seal failure or magnetic de-coupling.

Twin City Die Casting wanted an alternative filtration method, and that is when they decided to use the filters. The filters used consist of a filter housing with a fiberglass element installed on a stand pipe designed to trap fine particles. Twin City Die Casting uses a full flow arrangement of these filters.

For side stream installation, which is recommended by Liquid Process Systems, the inlet of the filter is installed close to the discharge of the pump (figure 2). The fluid is diverted through the filter, cleaned and discharged to the suction side of the same pump or to a low-pressure return line.

[Figure 2 ILLUSTRATION OMITTED]

Implementation of the filter consists of the fluid being drawn into the filter unit by tapping off the existing piping and diverting a percentage (usually about 10%) through the filter unit. The fluid is then cleaned and re-introduced down stream or to the suction side of the existing recirculation pumping system as the heating system is operating. All of the fluid passes through the filter at least 15 to 20 times per day.

Thus, instead of replacing fluids, they can be cleaned continuously and used with extended fluid life.

Organic heat transfer fluids are generally stable if operated below their thermal stability limit and not contaminated by agents from outside the system. Fluids generally are said to degrade when they are subjected to temperatures ranging from 150 [degrees] F to 750 [degrees] F (66 [degrees] C to 399 [degrees] C), which is common. As overheating and contamination occur, insolubles form. These contaminants deposit on the system and foul heat transfer surfaces. Sedimentation from the solids also causes plugging of pipes and heater element burnouts.

For maintenance, simply remove the contaminated filter element and insert the new one. Downtime is minimal. Initially, filter element change-out depends on the existing level of contamination. The life of the element can be from three to six months, depending on the cleanliness of the oil and on the operation (figure 3).

[Figure 3 ILLUSTRATION OMITTED]

Once in a while, a shaft seal will leak, but operation is said to be much more predictable and efficient now. Filtration is only as good as the scheduled maintenance.