The condensation of steam in liquids by means of S&K Direct Contact, Steam Heaters is a very efficient method of heating liquids. Since the steam and its condensate is mixed directly with the fluid, all of the heat in the incoming steam is utilized to heat the liquid. Where the addition of condensate to the mixture is not objectionable, this type of heater is ideal.
S&K manufactures various types of these heaters. The application will determine what particular type is most suitable. These Direct Contact, High Capacity Steam Heaters provide large quantities of hot water for delivery to a tank or reservoir. A temperature rise of 130ºF is possible under certain operating conditions. The hot water capacity is limited only by the maximum size of the heaters offered as standard items. Details on temperature and capacity are given for each type heater.
These heaters are simple in design, having no moving parts. Heating is continuous and fast. Inspection and routine maintenance are greatly facilitated by conveniently placed access ports. Because of high heating efficiency, a relatively small, lightweight size can be used to deliver a large supply of heated liquid. Injected water is broken up into fine particles by passing through spray nozzles or over trays and intimate mixing is obtained by the turbulence of the liquid steams. The thorough mixing provides for full condensation of the steam transferring maximum heat to the water.
Three piping connections – water inlet, steam inlet, and heated liquid outlet – are all that are necessary. These heaters are adaptable to the use of special materials to meet corrosive and other conditions. They can be furnished in cast iron, fabricated steel, alloy steel, Hastelloy, in any combination of these, or other materials.
The Type 323 Continuous Heater is suitable for operation within a wide range of conditions. It does not require a barometric leg. At atmospheric pressure and above, a temperature rise of 100ºF is obtainable. Hot water capacity ranges from 10 gpm to 240 gpm. The Type 323 Heater should not be used if air and other non-condensables are present.
Type 323 Heaters are the most compact in design and construction of the various types manufactured by S&K. Standard units are made with cast iron bodies and diffusers, and with bronze water nozzles, combining tubes and tail bushings.
The heater must be installed vertically and water flow must be started before steam flow. The water enters the unit through the top inlet at a pressure great enough to overcome back pressure and pressure drop within the unit. These two factors set the lower pressure limit of the inlet water. (Nozzles can be designed for any pressure above the lower limit.) Steam enters through the side inlet and is entrained by the water jet passing at high velocity through the combining tube. Temperature is controlled by throttling the steam.
Type 337 and 338 Heaters are “counter-current” types with the water and steam flowing in opposite (counter) directions. All operate effectively with internal pressures above and below atmospheric pressure. With typical units of medium size, hot water capacities range from 6 to 6,000 gpm. No limits on unit size have been set and, since capacities are determined by unit size and steam available, there are no limitations on hot water capacity. In conventional units, a water temperature rise of 130ºF is obtainable provided air is absent and other operating criteria are met.
As illustrated, Type 337 units consist of a cylindrical body with side vapor inlet, top water inlet, and spray nozzle to provide direct, intimate contact between water and steam. Type 338 units are similar but larger and have slightly different nozzles. In sizes up to 42 inches, the 338 type has flat heads at water inlet and discharge. In larger sizes, heads are dished as shown in Fig. 3.
Water is sprayed or discharged from the top of the heater. Steam enters from the vapor inlet and flows up through the water spray or “cascade”. Heating of the water is accomplished by the direct contact of steam and water and the resulting condensation of the steam.
The heaters shown also can be used as gas coolers. In such applications, dry gases are cooled by sensible heat transfer in which water is evaporated into the gas – as in the case of flue gas. Normally, the 337/338 operates at atmospheric pressure or above, but can be designed to produce hot water under vacuum conditions. In the vacuum mode, it is necessary to discharge heated water through a barometric discharge pipe.
The Type 326 Direct Contact Multi-Spray Heater is suitable for very large quantities of hot water, a top vapor inlet is required, and steam pressure is atmospheric or above. Type 326 Heaters will operate with a differential of 3 psi between inlet water pressure and the internal pressure. Flow variation is dependent upon the maximum pressure available. Under some operating conditions a temperature rise of 130°F is obtainable. Hot water capacities range from 350 gpm to 9000 gpm.
The body of the heater is made of cast iron or fabricated steel. Spray nozzles are bronze and are non-clogging provided inlet water is screened by 1⁄4 ” or 3⁄8 ” mesh. Ready access is provided by inspection ports opposite each nozzle. Heaters can be made of special materials as required.
Water is distributed peripherally to a series of converging spray nozzles which disperse the inlet water into very fine particles. Further dispersion is accomplished by a centrally placed deflection baffle. Steam enters at the top and passes through the water spray, condensing immediately and completely. The hot water is delivered to a tank through an outlet at the bottom of the heater. If internal pressure is below atmospheric pressure, a barometric leg, long enough to balance the pressure within the heater must be used to permit discharge of the hot water. The air vent prevents accumulation of non-condensables and balances the pressure of the heater. The Type 326 Heater is designed to prevent flooding, and to heat water close to the steam saturation temperature.
TERMINAL DIFFERENCE
(steam saturation temp. – water exit tamp.) This will vary with the type of heater used, the amount of non-condensables present, and temperature rise desired. The range is from 0º to 40ºF. Schutte & Koerting should be contacted for further details.
