Cooling Systems – Low Maintenance and Environmentally Friendly

Optimal temperature during the production process is often a critical factor for product quality. Steam jet cooling systems are environmentally friendly because they require only water or aqueous solutions instead of chemical cooling agents. Low-pressure steam (waste steam) can be used for operation instead of costly electricity. Steam jet cooling systems operate under vacuum corresponding to the vapor pressure of water at the cooling temperature. By means of vapor jet compressors, the amount of water evaporated (approximately 1.5 kg per kW of cooling capacity) is compressed to a higher temperature level and condensed together with the drive steam. Low-pressure steam (waste steam) can also be used as drive steam for vapor jet compressors. After the cooled water and cooling water have been degassed or as a result of leaks, inert gases are extracted by a vacuum pump or preferably a steam jet vacuum pump. Steam jet chillers are used to cool water or aqueous solutions from high temperature ranges down to nearly freezing temperature. The capacity range extends from approximately 100 kW to over 20,000 kW. Application examples include use in the chemical industry, food industry, plastics and paste industries, such as direct cooling of products like molding sand and paints, and preparation of cold water for use in air conditioning technology.

Operating Principle of Steam Jet Chillers

Steam jet chillers operate under vacuum according to the flash cooling principle. 1 Drive steam 2 Medium to be cooled 3 Cooled medium 4 Cooling water 5 Warmed cooling water A Expansion chamber B Vapor jet compressor C Condenser Figure 1: Operating principle of steam jet chiller Figure 1 shows the operating principle of the steam jet chiller. Due to its high heat of vaporization, water is suitable for this purpose. As system pressure decreases, the cooling effect increases. If very low temperatures are required and the condensation temperature of the flash steam is lower than the temperature of the cooling medium, the steam must be compressed so that it can condense at a higher pressure and temperature level. When vapor jet compressors are used for this purpose, the relevant systems are called steam jet cooling systems or steam jet chillers.

Steam Jet Chiller Design

Steam jet chillers are designed as single-stage units for very low cooling capacity or low cooling requirements. For higher cooling capacity and greater temperature differences, several cooling stages are arranged in series. Figure 2 shows a schematic drawing of a 3-stage steam jet chiller in bridge design. 1 Expansion chamber 2 Condenser 3 Jet pumps 4 Air removal vacuum pump 5 Collection tank 6 Re-cooling chamber 7 Circulation pumps

Figure 2: 3-stage steam jet chiller in bridge design.

Steam jet chillers consist of simple components such as expansion chamber, agitated or surface condenser, pipe lines, and vapor jet compressor. Therefore, they are easy to operate and always ready for use. Because they have only a few moving parts, they require very little maintenance. The cooling limit that can be achieved is determined by the freezing point of water, as long as there is no depression of the freezing point due to dissolved substances. Energy consumption values of multi-stage systems are low. Drive steam and condensed steam can be returned to the process. The heat of condensation is either expelled to the outside through a cooling tower or similar process, or transferred to a process requiring heat or another location with thermal requirements. Cooling of aggressive media can be easily achieved with a steam jet chiller. Due to their simple structure and lack of moving parts, steam jet compressors can be manufactured from any material used in engineering applications. There are essentially three different designs of steam jet chillers: • Compact design for lower capacities, • Column design for medium capacity and high capacities with minimal floor space, • Bridge design for high capacities. [gallery size="medium" ids="eyJ1cmwiOiJodHRwczpcL1wvd3d3LnR1cmtjaGVtLm5ldFwvd3AtY29udGVudFwvdXBsb2Fkc1wvMjAxOVwvMDlcL2dlYV8uanBnIiwidGl0bGUiOiJnZWFfIiwiY2FwdGlvbiI6IjxiPkZpZ3VyZSAzOiAyLXN0YWdlIHN0ZWFtIGpldCBjaGlsbGVyIGluIGNvbXBhY3QgZGVzaWduLCA8YnI+Y29vbGluZyBvZiA0NCBtXHUwMGIzXC9oIG9mIHdhdGVyIGZyb20gMzAgdG8gMTBcdTAwYjBDLiA8YnI+Q2hpbGxpbmcgY2FwYWNpdHk6IDEwMjUga1c8XC9iPiIsImFsdCI6IiIsImRlc2NyaXB0aW9uIjoiIn0=,eyJ1cmwiOiJodHRwczpcL1wvd3d3LnR1cmtjaGVtLm5ldFwvd3AtY29udGVudFwvdXBsb2Fkc1wvMjAxOVwvMDlcL2dlYV8xLmpwZyIsInRpdGxlIjoiQ29vbGluZyBTeXN0ZW1zIiwiY2FwdGlvbiI6IiIsImFsdCI6IkNvb2xpbmcgU3lzdGVtcyIsImRlc2NyaXB0aW9uIjoiIn0=,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"]

Applications

Steam jet chillers provide an excellent solution for cooling water used as cooling water to approximately 0°C. Installation of steam jet chillers is particularly easy in the following situations: • When steam and cooling water lines are already in place, • When hot water or steam (waste steam, vacuum or wet steam) can be supplied at a reasonable cost. The use of steam jet chillers is ideal in applications with relatively constant average cooling requirements or where variable cooling capacities are needed or there is a seasonal requirement. Steam jet chillers are generally well-suited for the 12°C / 6°C temperature required in air conditioning units. They can respond very quickly to changes in cooling requirements and are also ideal for use in batch processes. The required drive steam can be obtained from biogas, engine heat, and other sources.

Steam jet chillers have the following characteristics:

• Low investment costs, • Simple and robust design, • Instant response to changes in desired cooling capacity, • Very low maintenance and repair costs (minimal wear and tear due to few moving parts), • Reliable and safe to use, • Both direct and indirect cooling can be performed; in indirect cooling, water is almost always used as the cooling medium and is therefore easier to handle, • Very low cooled medium holding volume, • Fast and frequent system load changes, • Minimum electrical energy requirement, • Waste heat and flash steam are used as drive media, • Highly efficient in seasonal and/or batch operations.

Vapor Jet Compressors

Vapor jet compressors are jet pumps operated by a drive medium (Ṁ1) and are also known as ejectors. As GEA, we have many years of experience in the design and manufacture of ejectors and ejector systems.

1 Nozzle 2 Drive nozzle mixing inlet 3 Inlet cone 4 Throat 5 Diffuser

p₁ Drive steam pressure p₀ Suction pressure p Discharge pressure ps Speed of sound pressure Δp_v Shock wave Ṁ₁ Drive steam flow Ṁ₀ Suction flow Ṁ Entrained steam flow

Figure 6: Operating principle of vapor jet compressors and pressure differences along the flow path.

Adiabatic expansion of the drive medium (usually steam) occurs in the drive nozzle (2), thus obtaining a steam jet reaching several times the speed of sound. After passing through the drive nozzle, where pressure energy is converted to kinetic energy, the steam jet expands. This energy flow carries evaporated steam away from the medium to be cooled (suction flow Ṁ0) and directs it to the inlet header of the mixing nozzle (3). After passing through the throat of the mixing nozzle (4) and reaching the diffuser (5), the kinetic energy of the mixed steam flow is gradually converted back to potential energy; that is, the medium is compressed to a higher discharge pressure. Vapor jet compressors operate at high speeds and thus can handle the high volumes generated by steam under vacuum. İlker Damar Sales Manager Industrial Applications GEA Türkiye         Thilo Dietzmann Project Engineer Vacuum Systems GEA Germany       Andrea Heuser Marketing Manager Chemical Applications GEA Germany