Simple Solutions That Work! Issue 11

62 In general, a reciprocal-style air compressor will generate about 4 CFM per HP, with a screw-type compressor generating about 3.5 CFM per HP. This means that a 2,000-lb/minute heater potentially may require the equivalent of 45 HP. This is not an insignificant amount; many times compressed air is thought of as a standard resource that simply comes with the building, and this obviously is not the case. High-pressure, regenerative- type blowers can be used to fluidize the sand in electric- resistance type heaters at a lower energy cost in comparison to compressed air, but these blowers have comparatively high HP requirements per CFM. Sometimes the regen blowers are a good choice but the air generated can be as high as 150-175°F. While this is not a problem when heating, it can be problematic when only a small amount of heat is required, or if no heat is required at all and the fluidization is being used only to move the sand through the heater. Comparably sized, water-pipe-style heaters will require much less connected power. Fluidization pressure normally is supplied with a blower at about 5 HP for a small, 300-lb/ minute unit up to approximately 25-40 HP for a 2,000-lb/minute unit. Normally, heating is supplied by a gas-fired boiler, which requires very little power to run the water pump. Natural gas is known to be a very inexpensive heat source. The energy required to run a water-pipe system will need to be calculated for each application in a particular region, but easily can be as low as 10% of the cost of an electric-resistance type. Cooling normally is achieved with cooling water from a simple cooling tower, enclosed or not, but this cooled water also is very inexpensive once capital costs are covered. Many times, larger plants will have cooling water readily available plant-wide. HEATING AND COOLING Because the water-pipe style offers the added advantage of cooling sand that is too hot or heating sand that is too cold, greater efficiencies and higher production can be achieved in the mold- or coremaking processes. While difficult to quantify, molds and cores will be of higher quality and require lower binder additions if the sand temperature is consistent and repeatable at the mixer. The change from heating to cooling normally is seasonal, but depending on the size of the supply-silo and the source of the incoming sand, it may require both heating and cooling on the same day. For instance, if cold new sand is transported to the silo feeding the heater/cooler, it will be necessary to heat the sand to the desired set-point. If sand from shakeout or reclamation comes in behind the cold sand, cooling will be necessary. Obviously the goal is to control the variable incoming