Page 378 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

346 Applied Process Design for Chemical and Petrochemical Plants

Open type heaters Figure 6-4 shows two individual single-stage ejectors
Steamjet heaters (large capacity) discharging into a common surface after-condenser. The
steam condensate can be re-used from this installation.
• Moving Air and Gases (and Pump Priming)
Figures 6-5 and 6-6 illustrate two-stage ejector installa-
Using steam as the motive fluid tions with barometric and surface type inter-after con-
Steam jet blowers densers respectively. The discharge of the steam non-con-
Steam jet exhausters densables from the second stage jet of Figure 6-5 is
Steam jet thermo-compressors exhausted to the atmosphere, while in Figure 6-6 the
Single-stage vacuum pumps steam is condensed in the aftercondenser and, essentially,
Multi-stage vacuum pumps only non-condensables leave the vent of the aftercon-
Using air as the motive fluid denser. Figure 6- 7 A indicates a diagram of a three-stage
Air jet blowers barometric type installation.
Air jet exhausters Figure 6-7B illustrate a barometric refrigeration unit,
Single-stage vacuum pumps generating chilled water in the range of 34°F to 55°F for
process cooling. It uses steam ejectors to lower the chill
Air jet compressors tank's vapor pressure to establish boiling/evaporation of
Using gas as the motive fluid the water in the tanks and condenses the vapors released
Gas jet compressors by plant cooling water in the barometric condensing unit,
Using liquid as the motive fluid which is sealed through the vacuum leg into a "hot" well.
Water jet exhausters Figure 6-8 illustrates various arrangements of ejectors
Barometric condensers with inter and aftercondensers. The condensers can be
Low level condensers barometric or nonbarometric types.
,!\Tater jet eductors (small capacities) Note that in Figure 6-8 and Table 6-2 the letter desig-
• Handling Slurries and Granular Solids nations of the stages conform to the latest Standards of the
Heat Exchange Institute for Steam jet Vacuum Systems [ 11] .
Using steam as the motive fluid The letter designates the jet's stage position in the system.
Steam jet syphons Precondensers are recommended for any ejector sys-
Steam jet slurry heater tem when the pressure conditions and coolant tempera-
Single-stage vacuum pumps ture will allow condensation of vapors, thus reducing the
Using air as the motive fluid required design and operating load on the ejectors. This
Air jet exhausters is usually the situation when operating a distillation col-
Using liquid as the motive fluid umn under vacuum. The overhead vapors are condensed
Water jet eductors in a unit designed to operate at top column pressure, with
only the non-condensables and vapors remaining after
condensation passing to the ejector system.
Intercondensers are used to condense the steam from
Types
a preceding ejector stage, thus reducing the inlet quanti-
ty of vapor mixture to the following stage. This is a means
Ejectors may be single or multi-stage and also multi-jet
inside a single housing or stage. The extra stages, with or of increasing steam economy.
without interstage condensing of steam, allow the system Aftercondensers operate at atmospheric pressure.
to operate at lower absolute pressures than a single stage They do not affect the steam economy or ejector perfor-
unit. Various combinations of series of jets with no inter- mance, but they do avoid the nuisance of exhausting
condensing can be connected to jets with intercondensers steam to the atmosphere, thus, they allow steam to be
or aftercondensers to obtain various types of operation recovered. They also serve as silencers on the ejectors,
and steam economy. The condensers may be barometric and with barometric types they can absorb odors and cor-
or surface l)'Pe. rosive vapors.
Condenser tail pipes, used with any condenser, are
Figure 6-2 suggests a few of the many uses to which
ejector type units are used in industry. sealed with a 34-foot leg into a sump, or with a condensate
pump operating under vacuum on suction. With surface-
Figure 6-3 illustrates a single-stage non-condensing type condensers, the level may be sealed in a receiver with
ejector. In this type of installation the steam outlet from a float or other type of level control.
the ejector is either exhausted to atmosphere or on top of Thermocompressors are steam jet ejectors used to boost
water in a sump. low pressure or waste steam to a higher intermediate pres-