Nuclear Agent Removal
The ROWPU removes the majority of ions wit bout post treatment. The reverse osmosis (RO) removal characteristics for nuclear warfare agents are as follows: . 95.5% of iodine, leaving the nuclear cylinder to remove 4.5%.
. 99.7% of strontium, leaving the nuclear cylinder to remove .2%
. 98.% of cesium, leaving the nuclear cylinder to remove 1.2%.
Chemical Agent Removal
l GB-99.1%, leaving the chemical cylinder to remove .7%.
l VX-99.9%, leaving the chemical cylinder to remove .1%.
. BZ-99.9%, leaving the chemical cylinder to remove .1%.
l GD-99.7%, leaving the chemical cylinder remove .3%.
Biological Agent Removal
The ROWPU also removes biological agents from a water source. Reverse osmosis removal characteristics for various chemical agents do not exist. Any biological agent that is not removed by the ROWPU will be eliminated by the chlorine residual maintained in the product water.
WATER TREATMENT EQUIPMENT
The Utilitiesman may be called upon to select and set up various types of field water treatment equipment. You must be familiar with the theory of operation, the capabilities, the installation considerations, and the maintenance requirements of this equipment. This section covers four types of water treatment equipment. They are distillation, reverse osmosis, filtration, and disinfection units.
In areas where a satisfactory freshwater source cannot be located and existing water treatment facilities are not usable, the distillation process can be used to obtain fresh drinking water from brackish water, seawater, or water containing excessive amounts of dissolved solids. Distillation is effective for removing radioactive contaminants from water. Since the output of distillation equipment is limited and the process is expensive, its use is restricted to situations in which no other process is adequate. Continuous flow or batch type of water purification equipment is used whenever possible.
Theory of Operation
Distillation consists of heating water to form steam, separating the steam from the remaining water, and then cooling the steam so it becomes water again (fig. 9-12). As the water is heated to form steam or water vapor and the vapor is separated and then cooled, solids dissolved in the water do not vaporize but remain behind in the raw water. A large amount of heat that is not evidenced as a rise in temperature is required to change (vaporize) boiling water into steam. The process whereby latent heat is removed and steam becomes water is called condensation.
Figure 9-12.-Distillation in its simplest form.
Heat flows through the bottom of the evaporator, enters the water, and changes the water to steam. The steam is condensed in the condenser, its latent heat of vaporization being transferred to the water surrounding the tubes. A portion of the cooling water that has picked up heat in passing through the condenser is used as feedwater for the evaporator. All dissolved solids remain in the equipment and noncondensable gases are vented to the air so the resulting distillate is almost pure. Thus the distillation process is usefull in producing water of an extremely high purity and low in total solids,
Despite this high degree of purity, all distilled water must be disinfected before being consumed because of the possibility of recontamination during handling, In thermocompression distillation, the latent heat of
vaporization of steam is again used to produce additional steam. The pressure and temperature of the steam generated in the evaporator are raised by compressing the steam. The compressed steam passes to the condenser section where it condenses, giving up its latent heat and causing more steam to form in the evaporator. This steam is then compressed and the cycle repeated. The use of combination evaporator-condenser with a steam compressor creates a closed heat cycle, permitting the continued reuse of the latent heat of vaporization. The compressor is driven by a gasoline or diesel water-cooled engine.
Figure 9-13 shows the operation of a simple thermocompression distillation unit. Cold raw water flows through heat exchangers where it is heated almost to boiling by the outgoing streams of distillate and brine and by water from the engine that drives the compressor. The hot raw water flows into the evaporator-condenser and is
Figure 9-13.-Flow diagram-thermocompression distillation.
changed to steam by the steam condensing in the tubes. This involves the transfer of latent heat. The steam in the evaporator is drawn into the compressor where it is compressed and its temperature raised (from 212°F to 222°F). The compressed steam flows back through the coils in the evaporator-condenser where it transfers its latent heat through the walls of the coil into the water in the evaporator section. This transfer of latent heat causes the steam to condense in the coils and changes the water in the evaporator into steam. This cycle will continue as long as the compressor runs.