A key component of this success is the heater's controls. The plant manager controls the plant's output through the heater's control panel. The batchman sets the digital controller to a desired water temperature and then lets the heater do the rest of the work.
The unit was easy to install into the plant's flow. The plant automatically draws from a well into an aboveground storage tank. The operator controls a valve that allows the water to either flow into the water heater or directly into the mixing process.
On the coldest days, the well water is heated to temperatures of 140–160° F, or even higher, to overcome heat loss absorbed by cold aggregate and ambient temperature. This ensures that the mix can still be poured at optimum temperatures around 70° F. “The great thing about an on-demand system is that the batcher doesn't have to wait on hot water,” says Larimore.
And along with adequate water, the unit was economical to operate. “This heater costs about half as much to operate as a direct-fired water tank at one of our similarly-sized plants,” says the maintenance supervisor. “This was our first winter with the heater, so I don't think it's been a true test yet. But, I don't foresee any problems.”How it works
Direct-contact water heaters work very differently from direct-fired water tanks with fire tubes and from boilers. Typically, they are vertical cylinders with a section of diffusion material inside the top, a burner in the middle, and a collection area at the bottom. Water sprayed into the top of the heater migrates downward through the section of diffusion material, called packing.
Packing is typically made from stainless steel formed into rings of various shapes and sizes. These “rings” provide the surface area where heat is transferred to the water from burner gasses. As the water flows downward through the packing, hot burner gasses flow upward through the falling water. The heated water collects briefly in the tank's bottom and is pumped directly from there to the mixing equipment.
Unlike a direct-fired tank with a fire tube, there is no need to heat and store large quantities of water before it can be used. Direct-contact heaters heat the water on-demand. These types of heaters also take up less area than tanks. And unlike boilers, direct-contact heaters are not pressurized and require less maintenance.
There are two reasons direct-contact heaters are more efficient than direct-fired tanks with fire tubes. Their design allows a higher percentage of heat from the burner to be absorbed by the water. Fired boilers and direct-fired tanks have to maintain higher stack temperatures to prevent exhaust gasses from condensing. This would cause rust and eventually interfere with burner operation.
Higher stack temperatures mean more heat is being carried out of the heater. The direct-contact design readily allows water vapor in exhaust gasses to condense and mix with the rest of the heated water.
Another reason direct-contact heaters are more efficient is they don't have to maintain the temperature of several thousand gallons of water. Because water is being heated and used on-demand, the burner is fired to heat only the amount of water used, as it is used.
To learn more about the Firestorm direct-contact water heater, contact the manufacturer by telephone at 800-235-5200, or visit the Web sitewww.heatec.com, Also, visit Heatec at booth #N277 at World of Concrete.Visit the following manufacturers'
Web sites for more information on hot water systems:
American GeoThermal Inc., www.amgeo.com, WOC booth #N853.
Kemco Systems Inc., www.kemcosystems.com.
Ludell Mfg. Co., www.elliscorp.com, WOC booth #N2577.
Sioux Corp., www.sioux.com, WOC booth #N129.