In this process, the flash steam leaves the flash tank and enters the suction side of the ThermoCompressor. The actuator on the ThermoCompressor is at a split range with that of the blow-down control value. In this arrangement, the actuator is located on the ThermoCompressor controls, therefore the differential pressure only uses the motive steam when it is required.

During sheet break, the sheet is no longer on the dryers. The condensing load is therefore small, since there is no paper to dry and condense steams. Consequently the suction steam side is low, letting in higher pressure motive steam which then overheats the dryers to higher temperatures, as in a cascade system. Normally a selector switch is facilitated to allow the operator to terminate signals being sent to the ThermoCompressor, thereby shutting off the ThermoCompressor during extended sheet breaks.

The Closed Loop ThermoCompressor System does not have the capability to purge any non-condensables from the system. (A non-condensable bleed should therefore be installed to purge the system.)

Thermo-Compressor Type

The ThermoCompressor System is an essential application for many high-speed machines. Use of the ThermoCompressor device actually dates back to the early 1900's.

Basic construction of a ThermoCompressor consists of a cast steel body, diffuser section, nozzle and control-value type diaphragm operator. The nozzle area is usually of a fixed diameter.

The principle behind its operation is rather fundamental. The flash steam, provided from the flash tank is transformed into lower, suction pressure. The high-pressure or motive steam passes through the nozzle of the ThermoCompressor and expands in a suction chamber, where the pressure energy is then converted into velocity energy. When the steam leaves the nozzle, it passes through the suction chamber at velocities of approximately 1500 to 2500 FPM. The lower suction pressure steam is mixed and entrained.

Prepackaged auxiliary equipment

The use of pre-assembled equipment packages on our Dryer Drainage Systems provides you with substantial reductions in mill installation costs. The following skid-mounted modules are available:

Condensate Tank Assemblies
Thermo-Compressor-Skid Assemblies
Vacuum Pumps
Vacuum Condensers

Cascade Type

The conventional Cascade Type System normally uses two (2) steam groups on the paper machine, where the largest steam group represents the main section. The application of a flash tank allows the recovery of flash steam and lets it "cascade" to the following section. "Cascading" is naturally achieved since the following section, to which the steam cascades, must run at a much lower pressure. However, some limitations may occur on dryer-limited machines, due to this natural process. (Figure1 displays the typical operation of a Cascade System.)

The Cascading ThermoCompressor System

This system is recommended as an inexpensive method to purge non-condensables. Figure 4 illustrates the function of this arrangement.

The advantage of ThermoCompressors is that each steam section can be run as an independently-controlled group (i.e.: it is not dependent on any other specific group). ThermoCompressors should be sized very carefully for optimum operational results. They can be an excellent application for fast high-speed single-grade machines such as Newsprint, but do not function efficiently on paper machines that produce a wide range of basis weights on wide speed-ranges.

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