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12.50 CHAPTER TWELVE

showing through, or other indications that lining failure could occur in the foreseeable fu-
ture. If there is damage to the internals or vessel lining, this damage should be identified
and either repaired prior to putting the vessel back into service or scheduled for repair.
Once the unit has been emptied of resin and examined, it is ready to have the re-
placement resin installed. For small systems, it is practical to pour the resin through a fun-
nel into the open top of the tank. For larger systems, it is feasible but labor-intensive and
time-consuming to pour the resin in the top of the tank or to remove the resin from its
drum with buckets and pour the buckets into the tank. Various methods have been de-
vised for putting resin into tanks. One of the simplest is to use a water-powered eductor
to suck the resin straight out of the barrel and into the exchange tank. This method re-
quires a source of pressurized water to operate the eductor. Another convenient method
is to fill the resin drums with water and to use an air-operated diaphragm pump to pump
the resin as a slurry. It is relatively fast and can be performed by a single worker with-
out much labor. For very large systems, it is sometimes practical despite the extra cost to
have the resin delivered in a tanker truck and pumped directly from that truck into the
service vessel.

Disposal. Ion exchange resins themselves are nonhazardous and are generally suitable
for disposal as ordinary trash in a landfill. However, you must take into consideration the
ions held by the resin in determining its classification as a waste material. Resins that
have been used to remove toxic substances become toxic. If the regeneration is not able
to completely remove the contaminant from the resin, then the resin may have to be dis-
posed of as though it were the toxic substance contained therein. Local requirements vary,
and some disposal sites may not take ion exchange resins or may take ion exchange resins
only in limited quantities or only after leach tests confirm acceptability. Ion exchange
resins that are regenerated with acids or bases take on the characteristics of those chem-
icals and therefore may be considered hazardous as acids or bases. To avoid this, prior to
disposal, these resins should be thoroughly exhausted into the salt form such that their pH
is neutral. It is usually better to remove the excess water from the resin prior to disposal.
This reduces the weight and handling difficulty.

Reliability and Availability
Ion exchange systems are not known for having high availability. This is due to a num-
ber of causes. First, in single-tank systems, the equipment is periodically out of ser-
vice for regeneration. It is not uncommon to purchase three 50% capacity exchangers;
thus while one unit is in regeneration or off-line, for maintenance, the other two han-
dle the load. It is prudent in larger systems to have at least one spare exchange tank
that is ready to be placed in service, should an unforeseen problem occur with a unit
in service.
By far the biggest factor in the unscheduled outage of ion exchange systems is the
chemical dilution systems for the regeneration flows. All regenerant chemicals are cor-
rosive; some are very corrosive, and if they are not carefully handled or if spills are not
promptly cleaned up, the area of the chemical dilution stations deteriorates. Although most
equipment vendors will provide spare chemical pumps, they usually do not provide the
spare dilution stations. Since the dilution station is one of the most likely parts of the sys-
tem to fail, this failure will cause an unscheduled outage of the equipment. For central-
ized ion exchange systems, the addition of a very large treated water storage tank hold-
ing 8 to 24 h of treated water volume at the normal flow rate helps to improve the
availability of treated water and overcome reliability problems. Overall, a single ion ex-
change tank will probably not be available more than 90% of the time and perhaps as lit-