COOLING SYSTEMS AND LUBRICANTS

 

COOLING SYSTEMS AND LUBRICANTS

Our company En-Ser Contracting&Trade Co., has been mainly involved in the field of Cooling Compressors and Cold Room lubricants for the last twenty five years. Particularly, after the 1990s, parallel to the increase of research and development on cooling compressors, more efficient systems have been developed resulting in lower operational costs but also needing new types of cooling lubricants. In our country, besides usage of new generation ammonia gas cooling compressors, with screw or piston systems, usage of new types of freon gas compressors are also common. With less frequency, carbon dioxide compressors can also be seen in the industry. Ammonia compressors are mostly seen in large food-processing and cold preservation sectors, together with shock freezing industries especially in rapidly perishable groups such as fruits, vegetables and also in milk, meat and pharmaceutical preservation fields. As to the GWP (Global Warming Potential) and ODP (Ozone Depletion Potential), freon gases such as HFC (Hydrofluorocarbon), CFC (Chlorofluorocarbon) have more negative effect on the environment than ammonia gas, which has almost zero effect on the environment and therefore is mostly preferred in line with the Kyoto Protocol. On the other hand, ammonia gas compressors are proposed for mostly large systems, since these systems are not appropriate for mobile installations. In freon gas compressors, the least GWP and ODP depletion can be maintained only by usage of R600 (Isobutanes), which are mostly utilized in home and commercial freezers and shock coolers. Other freon gases such as R134a is mostly used in vehicle air conditioners, R290 in heat pumps, R404a, R406a or R410 are used in larger air conditioners and coolers. This last group of gases are usually combined with HCFC (Hydrochlorofluorocarbon) gases formed to reduce climate effects. The following lubricants are commonly used in accordance with the operational requirements and in line with compressor types:

• Naphthenic Based Lubricants

Naphthenic base lubricants, which are mineral oils, are produced with vacuum distillation method in refineries, which are later refined with solvent in order to eliminate heavy components such as nitrogen, sulphur and asphaltic residues, and lastly by applying 800 atmosphere pressure to detach wax remnants almost to 85 percent from the lubricant. Naphthenic oil series are mostly used in older technology ammonia cooling compressors (before the 1980s) and also with R-22, R-12 Freon gas compressors. In these compressors, usually the maximum operational cooling temperatures do not exceed -30°C. These oils are introduced to users after enriching and strengthening with adequate additives.

• HT (Hydrogen Technology Applied) Semi-Synthetic Lubricants

These types of oils are double treated with 400°C and under 3000 atmosphere pressure, in order to eliminate nitrogen, sulphur and other aromatic components from the base mineral oil to attain 99.9 percent purified lubricant. At the last stage, they are strengthened by synthetic additives such as pour point depressants, viscosity stabilizers and anti-corrosives to give best performance under harsh operational conditions. In these lubricants, about 97 percent of the lubricant consists of the HT purified base lubricant and about 3-5 percent consists of the above mentioned synthetic additives, therefore they are mostly named as semi-synthetic lubricants. These lubricants can be used up to -40°C to -42°C degrees in compressor operations.

• Naphthenic Based Semi Synthetic Lubricants

Base naphthenic oils produced with solvent application are detached from wax ingredients are later mixed with full synthetic PAO (Polyalphaolefin) in order to produce a resistant structure to harsh operational conditions, which are also strengthened with synthetic additives. Such oils are usually used up to -39°C operational degrees in ammonia cooling.

• PAB Based Lubricants

Such oils are fully synthetic oils produced with fully synthetic PAB (Polyalkylbenzene), which can resist very harsh conditions and can be used up to -45°C operational conditions • PAG Based Lubricants Such oils are produced with fully synthetic PAG (Polyalkylglycol), to resist harder operational conditions and can be used in compressors with mostly high compression pressures and high exhaust temperatures. They can also face higher cooling temperatures. - In most ammonia compressors, the preferred lubricants are at 68 cst. viscosity. The lubricants used in freon compressors vary in accordance with compressor type and compressor manufacturer's advice. These lubricants are generally POE (Polyol ester based) fully synthetic lubricants and should also be selected in line with the freon gas type used in the compressor. For instance, freon compressors with R134a, R404a or R410a that operate up to -45°C operational temperatures, the appropriate viscosity of lubricant should be around 32 cst. With similar gases, but -42°C operational temperatures, the required viscosity will be 46 cst. and with -39°C temperature, the viscosity of lubricant would be close to 68 cst. In cooling systems, cold room temperatures may vary from +4°C up to -55°C range. In consistency with the operational degrees and conditions, the types of lubricants and greases should also be selected correctly. The equipment or processing devices employed in the cooling tunnels and rooms should use synthetic and mostly food certified lubricants with varying pour points from -30°C up to -70°C degrees. In such environment, sizeable cooling fans,

IQF (Individually Quick Freezing Equipment) and shock tunnel equipment, such as rolling bands etc. need special high pour point lubricants with generally food grade characteristics, namely NSF-H1 and NSF-H3 coded certificates.

In the cold logistics area, generally employed air conditioners and coolers use R404a, R408a, R410a freon gases. In some cool chains, cold boxes of various sizes are also used together with freon gas compressors. In such systems the break down of the cold chain should not be allowed, especially for fruits, vegetables, meat and milk groups, otherwise, big quality and commercial losses may be incurred due to bacteriological destruction and aromatic losses in these products. Currently, most of the cooling lubricants are imported to Turkey. Even though, in the last years, few companies which follow current technologies and appropriate equipment, started to produce ammonia compressor oils. Lubricants production requires a very sensitive application of production methods, appropriate selection of the additives and continuous follow up with laboratory analysis of the product specifications along with customer feedback. Kudret Tan - Senior Industrial Engineer - MSc. Industrial Engineer -En-Ser Contracting and Trade Co. - En-Ser Contracting and Trade Co.