Pollution Prevention and Control Technologies for Plating
Section 3 - Chemical Recovery
3.2 ATMOSPHERIC EVAPORATORS
3.2.4 Technology/Equipment Description
The equipment described in this section is manufactured by four
firms that responded to the Vendors Survey. Three of these companies
represent approximately 90% of the total number of atmospheric
evaporators purchased by the respondents of the Users Survey (not
counting home-made units or in cases where the manufacturer was
The manufacture of atmospheric evaporators most often found in
the Users Survey data is Poly Products Corporation. They manufacture
four different models: ET-II Junior, ET-II, ET-III and ET-III-W.
The ET-II Junior, ET-II, and ET-III are progressively larger units
of the same design. The ET-III-W has a modified design, intended
for use with solutions that have a high solids content. Each model
has the same basic appearance and operating principles (refer
back to Exhibit 3-3). During operation,
pumped solution is circulated at approximately 10 to 45 gpm from
the process tank or transfer tank to the unit and is gravity drained
back to the tank. In the evaporator, solution is sprayed onto
700 to 1,000 ft2 of evaporative panels to humidify the blower
air that is forced through these panels. The air is provided by
a blower sized from 1/2 to 1-1/2 hp, depending on the model. The
humid air then passes through a chevron mist eliminator to remove
entrapped chemical solution droplets and is ducted to the outdoors.
Poly Products offers an optional mesh pad mist eliminator to further
decrease chemical emissions. The ET units are manufactured of
molded polyethylene. The largest ET unit occupies a floor space
of 48 in. x 34 in. All models have maximum air temperature limits
of 104oF and solution limits of 160oF (ref. Poly Products file).
Techmatic Inc. manufactures the MAX-EVAP™. There are four
models available: MAX-EVAP, Super MAX-EVAP, MAX-EVAP Cr and Super
MAX-EVAP Cr. The MAX-EVAP and Super MAX-EVAP are general purpose
units with advertised evaporation rates of 50 to 60 gph and 80
to 90 gph, respectively. The bodies of these units are manufactured
from polyethylene. The MAX-EVAP Cr and Super MAX-EVAP Cr are designed
specifically for hexavalent chromium plating solutions. These
two models are manufactured from steel and are lined with Koroseal
(PVC). As with the operation of the Poly Products line, solution
is circulated from the process tank or transfer tank to the unit
and is gravity drained back to that tank. In the evaporator, solution
is sprayed onto 5 to 10 ft3 of polyethylene packing. Air is drawn
through the unit by the shop's existing ventilation system or
air movement is provided by an optional blower. The exhaust air
passes through a "vertical extruded mist eliminator"
(not defined by manufacturer) to remove chemical mists. The MAX-EVAP
unit occupies a floor space of 63 in. x 21 in. and has a height
of 31 in. (blower option measures 55 in. high) (ref. Techmatic
Kinetic Recovery manufactures a unit with a somewhat different
design than the two previously discussed units. With the Kinetic
Recovery unit (Exhibit 3-6) the process
solution is pumped from its tank up to the liquid distributor
of the evaporator which is located at the top of the cylinder.
The liquid trickles over a tower packing down to the bottom drain
of the cylinder and returns to the process tank. A blower, located
at the bottom of the cylinder, blows air (300 cfm) upward through
the packing to the top of the evaporator. When the air goes through
the packing (pressure drop 0.3 in. of superfacial vapor velocity
of 1.5 fps) it becomes saturated with vapor from the process solution.
The cylindrical design improves air flow distribution by reducing
dead space. On the top of the cylinder there is a vent transition
which contains a mist eliminator (12 in. flexi-chevron). There
are two view ports located on the unit, one at the liquid distributor
and another below the packing. The basic Kinetic Recovery unit
is manufactured from polypropylene and they offer construction
in PVDF. The PVDF unit operates with a maximum solution temperature
NAPCO manufactures atmospheric evaporators with two basic designs:
(1) cross-flow air pattern and (2) vertical air flow pattern.
Both types of units are normally constructed of polyethylene,
but a variety of plastics are also available, depending on the
customers needs. The basic NAPCO unit consists of a blower, recirculation
pump, high surface area packing and demister baffling. Numerous
options are available, including heating coils, temperature controls,
level controls and make-up solenoids and pumps. Their standard
size units range from 10 gpm process feed/1,200 cfm air flow (NAPVAP
Jr) to 30 gpm process feed/4,000 cfm air flow (NAPVAP Sr). NAPCO
has been marketing their equipment to the plating industry since
1985 and have sold approximately 160 units to 100 different plating
For each of these four commercial evaporators, the heat used for
evaporation comes from the plating or transfer tank (unless a
heating coil option is specified). Heat taken from the plating
bath must be replaced by the tank heating system (e.g., immersion
heaters or steam system) in order to maintain the operating temperature
of the bath. Most tank heating systems are designed to provide
a quick heat-up and are underutilized after the operating temperature
is maintained. Therefore, auxiliary tank heating equipment is
usually not necessary when an atmospheric evaporator is installed
(unless a transfer tank is also installed). However, each potential
installation should be evaluated before purchasing evaporative
equipment. Nomographs and methods of calculating tank heating
requirements are available in electroplating engineering references
(e.g., ref. 341).
The atmospheric evaporators previously discussed are used primarily
for chemical recovery, but are occasionally applied to waste concentration.
Some evaporators are designed specifically for waste concentration.
Two such units include the Technotreat Wastewater Evaporator and
the Samsco Water Evaporator.
The Technotreat unit consists of an enclosed carbon steel (stainless
steel available) tank equipped with electric immersion heaters
(stainless steel or titanium). Liquid waste is fed into the evaporator
by a feed pump from a drum or storage tank. The solution level
in the evaporator is maintained by a level switch which activates
the feed pump. The steam is vented by an assisting electric blower.
As water is evaporated, the waste is concentrated. Oil floats
to the top and is drawn off periodically. Sludge and viscous materials
are removed through a bottom drain. The Technotreat unit comes
in 100 and 200 gpd capacities. The range of costs is approximately
$10,000 to $15,000 for the standard materials of construction
The SAMCO Water Evaporator combines direct heating and air flow.
The unit consists of an enclosed tank (carbon steel or 304 or
316 stainless steel) that contains a serpentine gas-fired heat
exchanger and blower (530 cfm to 2,000 cfm) that draws air in
through both the burner and an opening in the top of the tank.
In operation, solution is fed to the tank in either a batch or
continuous mode. The solution is heated to boiling (approximately
212oF) by the heat exchanger. The action of the blower draws air
across the surface of the heated liquid, sweeping away water vapor
as it breaks to the surface. The moisture-saturated air and the
flue gases leave the tank via separate passages and are joined
together at the blower entrance. The two air streams are mixed
in the blower and released up a stack. Free oils that float on
the surface of the liquid overflow a trough into an external waste
receptacle. Solids that settle onto the sloping bottom of the
tank are removed via a clean-out port. The SAMCO Water Evaporator
comes in three capacities: 15 gph, 33 gph and 63 gph. The area
dimensions of the largest unit are 65 in. x 68 in.
Installation of an atmospheric evaporator is a relatively easy
task with the exception of the ventilation ducting. The basic
units are shipped pre-piped and preassembled. For ventilation,
ductwork is usually routed directly to the outdoors through a
roof penetration. Alternatively, the exhaust of the evaporator
can be connected by ductwork to an existing ventilation system.
In this case, an evaporation system blower is unnecessary and
the air would be drawn through the evaporation chamber rather
than being pushed or blown through. As discussed in Section 3.2.3,
this configuration is occasionally used with hard chromium plating.
Installation and operation of an atmospheric evaporator may require
a new air permit or revisions to an existing air permit.
Next Section|Main Table of Contents|Section 3