Getting Ideas for Energy Management Opportunities

2.4.2 Air management

Commonly, foundries have problems with the ventilation of work zones. Usually, there is an imbalance between fresh air and exhaust air. The problem is often compounded by a dusty atmosphere and sometimes high carbon monoxide (CO) content. For this reason, the construction of foundries traditionally allowed for ample sizing of roof monitors and exhaust stacks. That was often done with
little thought on the proper location of these vents or on the distribution of air make-up.

Excessive air exhaust results in high under-pressure in the building and draught problems. In production areas inside foundries, the existence of too many exhaust points and the lack of a system for air supply may have created this negative pressure. At the same time that the production creates a heat surplus (wasted by the exhausts), additional heat must be supplied by other means to the fresh make-up air being brought in from the outside in the winter. To add to the waste, city water may be sewered after providing just once-through cooling.

Here are a few examples of how others have dealt with the problem:

Do not undermine the function of a well-designed ventilation system by leaving doors and windows open unnecessarily – otherwise it will never work!

A foundry dealt with dusty and hot exhalants and its ventilation needs in a combined way: flue gases were passed through scrubber/heat exchanger, and the incoming air was preheated in the winter. The incoming ventilation air system adjusted to the changing needs by regulating the fan’s capacity in the inlet section. This was regulated by monitoring the air pressure in the incoming air channel. The air exhaust system had suction points located in the most polluted areas of the plant, with separate fans for each of the zones. The exhaust fans also had speed regulators. The whole system, connected to a central monitoring system and controlled by a PC, obtained a balance between the inlet and outlet sections of the total ventilation system. The energy costs for the plant ventilation were halved as the result and the incoming air was no longer polluted with the dusty exhalants as before.

Another plant opted for a simpler approach, but still divided the plant into separate ventilation zones. Only the sections where operations were taking place were fully ventilated; others, where no work was going on, had ventilation valves only partly open to allow minor ventilation.

Unnecessary exhaust of 10 000 cfm translates to about $1,500/yr. in heating costs!

Other EMOs
Housekeeping

  • Keep the doors/loading bays closed to allow the ventilation system to work properly.
  • Switch off ventilation and/or heating when not required.
  • Shut down dust collection, ventilation and make-up air when not required.
  • Assign someone (e.g., maintenance) to turn off the fans, close the vents, etc., at the end of the week. Prepare a checklist so that nothing is overlooked.
  • Conversely, put someone in charge to switch on the ventilation system at the beginning of the workweek.
  • Incapacitate some non-essential exhaust fans during the winter months (take the fuses out).
  • Eliminate leaks and pressure loss points in supply and return air systems.
  • Clean or change dirty air filters regularly.
  • Examine your present system – perhaps the original dust collection/exhaust system was designed to handle larger volumes of air than necessary for ordinary plant operations. Maybe some of the fans could be taken off-line, at zero cost, for immediate benefits of:
    • Reduced maintenance;
    • Lower energy costs;
    • Reduced emissions; and
    • Reduced noise.
      You can easily verify this by turning the selected fans off and watching what happens.
  • Pay attention to the upkeep of your baghouse/dust collection system; monitor both its integrity and resistance (i.e., proper functioning) by a differential pressure gauge (e.g., water column gauge).
  • Monitor CO (carbon monoxide) levels at head level around pouring and shakeout, and corners away from these areas. It will give an additional indication of the ventilation effectiveness.
  • Keep the motors on forklift trucks and other foundry vehicles well tuned, to reduce the excessive release of CO into the foundry atmosphere, which increases ventilation demand.
  • Watch for “shortcutting” of heated make-up air directly to a nearby exhaust fan.
  • Check the temperatures of indoor air high up in the foundry roof area for potential to recapture the heat from relatively clean areas.
  • Delay the start of foundry ventilation at the beginning of operation until the heat of melting, pouring, shakeout, etc., has warmed the air inside.
  • Where required, cut small openings into large doors to allow the passage of forklift trucks; use transparent curtains to prevent continuous blasts of cold air from outside.

Low cost

  • Install strategically located hoods over dusty/hot areas. Make sure that they have ample dimensions so that the heat or dust does not escape into the general space.
  • Tie the exhaust fans from dusty areas, e.g., the mould shakeout, to the activity: have it on only during the dust generation period (which is usually intermittent); throttle the fans down during idle periods. Another examples of this application of modulated ventilation is in blast rooms or oxy-gas burn-off stations, during charging of an induction furnace, floor mould pouring and cooling, etc.
  • Recapture the heat that accumulates high up in the foundry rafters – push it down in the winter (filter it if required) and control it thermostatically should the outside temperatures be extremely low.
  • Fit the exhaust fans with variable speed drives to match the ventilation rate to the need.
  • Investigate whether you can supply outside air directly to a particular operation to conserve the heated plant make-up air (e.g., for air classifiers for wheelabrators; shot-blast rooms).
  • Install high-velocity air curtains at loading bays and other large openings.
  • Consider installing double-door vestibules or windbreaks in northwest locations of the openings.

Retrofit; high cost

  • Replace the general ventilation of the entire area with locally situated, hooded exhausts from areas that need to be ventilated (e.g., over bake-core making machines, furnaces, ladles and pouring stations, especially in non-ferrous foundries).
  • Fresh air of constant temperature can be provided in a foundry by the installation of a new ventilation system using a rotary heat exchanger. The warm exhaust air heats the incoming air in the exchanger. The temperature is controlled by the number of revolutions of the exchanger (payback in an iron foundry is about two years).

 

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