Business: Industrial

Getting Ideas for Energy Management Opportunities
2.2.4 Managing water

There are two aspects to water management in a foundry: conservation of use,
i.e., of volume used, and utilization of the heat the water carries.

The
effort to manage water should start with preparing water balance. The locations
and flow rates of all water uses in the plant can be measured, and if the water
meters are not available, as is commonly the case in many small
foundries, use estimates. The mains water pressure, known diameter of the mains,
and often a five-gallon bucket and a stopwatch can be used as the improvised
tools to provide a reasonably accurate picture. Water temperatures should be
measured. The information should be analysed for wasteful, non-productive usage
and excessive flows. A picture should emerge about what stream can be used
where, whether water reuse is possible and for what purposes, and where there
is a potential for heat transfer. With successful launching of water conservation
initiatives,
justifications may become available for installing more water flow meters elsewhere
in the foundry.

Leaking valves and taps, loose joints and leaking pipes can
cost the foundry a lot of money over time. Chances are that in a foundry there
may be several leaks at any given time and the losses add up. Associated costs
of electricity
to operate pumps, fans, water treatment costs and maintenance increase the
financial losses further.

Annual water costs in a foundry are substantially
lower than energy costs, but water conservation is a tangible, high-visibility
action to which everybody can relate and which everybody would likely support.
Undoubtedly, there are opportunities for conservation in any foundry. In the
processes, water discharged
from one operation could be piped into wet scrubbers, or mullers for sand conditioning,
etc.

A foundry may have several water systems, such as process cooling water,
potable water, domestic hot water, boiler feedwater. They have similar inefficiencies
and, because of the water heat content, similar energy management opportunities.
Cooling water is used for mould sand reclamation, electric arc furnace or induction
furnace cooling, as a heat extraction medium in furnace or oven flue gases,
in shell mould and shell core machines, in mould units’ hydraulic systems,
in permanent moulds cooling, in quenchers, in air compressors, etc. The water
should be recirculated as many times as possible through these operations to
prevent waste. For that to occur, however, the water itself needs to be cooled
down.

Open systems such as evaporative coolers, i.e., cooling towers, are commonly
used. They need additional energy to drive the fans that move the air through
as well as water make-up to compensate for evaporation, drifts and the necessary
blowdowns. The water has to be treated to prevent scale and slime formation
and corrosion. Cooling towers cool down the returning water to a level that
is usually about 6°C (10°F) above the ambient wet-bulb temperature.

Closed-loop
mechanical water chillers use the refrigerant condensing coil to extract the
heat. They conserve water, produce very cold water and eliminate the need for
water-conditioning chemicals, but they are more expensive to install and run.
In a foundry, they may find an application for induction furnace coil
cooling, for example, where the predictability of the water incoming temperature
allows for close control of the furnace.

The cooling of air compressors also
requires close control of the cooling water temperature. Both undercooling
and overcooling can cause serious mechanical
damage to an air compressor, and it is best to consult with the air compressor
manufacturer.

In all projects involving the heat content of water, proper insulation
of tanks and pipes is necessary. The hot water energy potential can provide
useful service
in space heating, steam generation, and tempering make up air as well as through
the use of heat pumps for air conditioning.

Other EMOs
Housekeeping

• Examine water use patterns and reduce water consumption to the minimum
  necessary.
• Maintain
  the system; stop leaks promptly.
• Reduce pump-operating time where possible.
• Instil good housekeeping practices
  in all employees.
• Do not let the eyewash fountains run as a drinking water source;
  provide
  drinking fountains instead.
• Remove stagnant, redundant branches of the water distribution
  network.

Low cost

• Re-use and/or recirculate cooling waters and process waters imaginatively
  (e.g., use a pump seal water to serve as an air-conditioning unit). Use process
  or cooling water as a heat-exchange medium in your ventilation or heating system.
  Consider placing a water/air heat exchanger system inside the
  foundry to help
  with the heating load in the winter, etc.
• Collect uncontaminated “wasted” water
  if the rate of its generation exceeds the rate of the immediate reuse,
  rather than emptying it down
  the drain. Install an inexpensive fibre reinforced plastic off-the-shelf tank
  or a second-hand vessel for the collection and use of the water later. Use
  these collection vessels to even out the supply/demand ratio in your water
  multiple reuse
  projects.
• Reduce water heat loss or gain by proper insulation.
• Install water system expansion
  tanks on closed loop systems, to serve
  two purposes: when the water is hot, waste through relief valves will be
  prevented. When the water is cold, the contracted volume would normally demand
  make-up water to keep the system filled.
• Reduce friction losses and the associated pressure drops by streamlining
  and correct-sizing of water pipes.
• Review correct size and choice of water pumps.
• Install water-flow regulators
  for sanitary uses; delayed closing or timed flow taps on hand wash basins
  and reduced-flow shower heads.
• Install the European-type on-demand gas water heaters
  for sanitary use (as one foundry did).
• Limit the use of make-up water to critical
  tasks, such as cooling of fan bearings in heat-treating ovens.

Retrofit; high
cost

• Use a closed loop, “dry” cooling system for electric induction
  furnace cooling, cooling of permanent dies, etc.
• Implement a water
  system with multiple re-uses of process water on the heat cascading principle.
• Consider
  employing heat pumps for the combined application of heat extraction and
  provision of chilling to process water and other fluids.
• Consider using waste heat to
  drive the waste-water evaporator, for sludge disposal.

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