Steam Jet Heaters
Steam Jet Heaters utilize the principal to mix steam with a cold liquid uniformly. Operation is efficient because the heat in the steam is absorbed by the liquid being heated to approximately 10% of liquid saturation temperature. The jet action produces agitation and circulation, eliminating the need for other equipment to accomplish these functions in most applications.
Basically, all of these Jet Heaters have a nozzle or orifice arrangement, a diffuser, and body (which in some cases consists only of bracing to hold nozzle and diffuser in position). In operation, jet heaters use steam (or steam and water under pressure) as the motive force to entrain, mix with, heat, and pump (or circulate) the suction liquid.
The liquid under pressure attains a high velocity passing through the nozzle. Steam enters through a series of nozzles in the combining tube and an intimate mixing of the liquid and steam occurs in the throat region. The liquid absorbs all of the heat of the steam. Under normal conditions no loss in water pressure occurs. In certain cases, this water can be operated against back pressures higher than either the supply water pressure or steam pressure.
These heaters can eliminate mechanical pumps, resistance or bayonet heaters and containment vessels. These units have a low initial cost, limited moving parts and are easy to install and require little or no maintenance.
Typical Liquid Eductor Heater Units
There are several types of liquid heating eductors designed to heat over a variety of conditions. Because of the diversity of applications for the units, the motive and heating ports may be in different locations. It is important for proper operation of the units that the liquid and steam be connected to the proper ports. The following models of eductors can be used in heating applications: ULJ, MLE, and MLH. On all of these units the liquid to be heated enters the motive connection.
Where can Liquid Heating Eductors be Used?
Eductors have been used to successfully heat liquids in many industries and processes. The units can heat in-line or in-tank to achieve results that will improve your process. These units are used in the following industries: Pulp and Paper, Chemical, Petroleum, Dairy, Agriculture, and Breweries. Typical applications include: sterilization, cooking, heated wash down sprays, heating solutions, pasteurization in-line, mixing while heating, activating temperature controlled substances, and maintenance of tempering vessels.
Why are eductors chosen for HEATING applications ?
Small physical size – Heating done completely within piping systems.
Low cost of installation – Foundations and wiring are not required.
Integral Gage Ports – Enables rapid troubleshooting.
No moving parts – Reduced maintenance.
ASME/ANSI B16.5 Rating – Enables ANSI rating of entire systems.
No packing glands – Reduced maintenance.
Lubrication is not required – Reduced maintenance.
Body as strong as piping – Handles normal piping stresses.
Wide variety of connection types available – Male/Female NPT, Butt/Socket Weld, Flanged, Silbraze, Victaulic
Properly installed eductors require few shutdown procedures – Ease of control for intermittent operations
Hex mounting on body – Easy mounting to piping.
Low relative cost for exotic materials – The no moving parts feature makes it easy and quick to obtain exotic materials. These materials will not affect the performance of the units.
Longer service life – The lack of moving parts means many units will operate for years without affecting performance.
O-Ring sealed body/nozzle joint – Bubble tight seal, easy effective maintenance.
Use of sources normally considered waste – In many cases, steam can be used for heating with pressures as low as 1 or 2 PSIG. This allows you to gain value from a resource normally vented or returned to your boiler.
Smooth body flow passages – High efficiency and flows.
Economical use of waste steam – Low pressure steam still contains substantial heating value, all of which is used.
How to Use Eductors for Heating in Process Lines Using Liquid as the Motivating Stream
The following models of eductors can be used as heating devices using pressurized liquid as the motive force for the process: MLH, MLE, ULJ. These units operate over a variety of conditions.
The models MLE and MLH will pull more steam for a given set of pressure conditions. They require a larger pressure drop through the eductor, but it results in a higher temperature rise through the eductor per pass. These units are generally used when the system requires a single pass through the eductor. If they are operated intermittently, the pressure drop will increase when the steam is shut off. When using low pressure steam for heating, it is recommended that the motive liquid temperature in these units not exceed 100°F. Higher incoming temperatures should be thoroughly evaluated to avoid objectionable noise and water hammer. To determine the actual operating parameters of each unit, refer to the performance table for that unit.
The model ULJ generally requires a steam pressure greater than the liquid pressure being used. It also produces less pressure
drop on the liquid, but there is a lower temperature rise for the liquid medium, as the lower steam flows contain less total BTUs. These models are designed so that they can be used on a multiple pass system. Many times these units are used to heat jackets on reactors or other systems where low pressure drops in the liquid lines are required or where a small temperature increase per pass is required. The lower amount of steam injected per pass allows these units to heat to higher final temperatures. Also, the liquid pressure drop remains small in these units when the steam flow is shut off.
The units, listed in general order of largest to smallest temperature rise and pressure drop, are: MLE, MLH, ULJ. These units are available for use to heat in-line, producing hot liquids for spray cleaning operations, heating liquids for jacketing on reactors or heat exchangers, cooking or sterilizing in-line.
When used with a temperature probe and a steam control valve, the eductor will result in an almost instant temperature adjustment. The lag time of the temperature probe and valve will affect the performance of the system lag more than the eductor itself.
General Rules for Selecting Eductors
- Is the steam pressure lower than the liquid pressure? If the answer is yes, choose one of the following eductors: MLE, MLH. These units will function pulling a low pressure steam into a higher pressure liquid stream.
- If the unit is to be used on a recirculating stream, consider the ULJ unit.
- If the steam pressure is higher than the liquid, consider the ULJ.
- If low pressure drop is allowed on the liquid stream, consider the ULJ.
Specific applications for inline heaters include: circulating cleaning solutions, pasteurization, producing scalding sprays, sterilization, heating water, blanching, exchanging heat, degreasing, heating slurries, laundering, cooking, pickling, bonderizing, quenching and tempering. Specific applications for open tank heaters include cooking grain, cooking mash, cooking starch, heating and circulating, mixing.