Simple Solutions That Work! Issue 11

Continued on next page 61 Water Pipe Based Heaters Since the water pipe based heater design units are much larger, their size as well as substantially higher weight will need to be taken into account. Since the retention time of the water pipe based heaters is much longer than the electric- resistance heater, the weight is substantially higher. The weight of the heater itself as well as the amount of sand in it are added together to calculate the necessary support. With the inlet at the top on one end of the heater and the discharge at the bottom of the other, the elevation requirements are somewhat greater than the electric-resistance design. If the silo is connected directly to the inlet, the discharge will normally extend beyond the footprint of the silo support structure. In new installations, this is not difficult to design around – in replacement or installations in existing facilities, this can be problematic. Elevation is always at a premium in any installation like this, but there are a number of design techniques that can be used to account for a lack of elevation which will not be addressed in this article. The support structure may be of sufficient strength to include the additional weight of the water pipe style heater, but this additional weight should be carefully calculated into the support structure to be sure it is sufficient and still have a reasonable safety factor. As with the electric-resistance type heater, it is important that this heater is supported in such a way that all service, inspection, and maintenance procedures can be performed quickly and safely. Normally the design of the water pipe design does not allow for support directly under the unit, but this will vary from manufacturer to manufacturer. As with the electric-resistance design, a carefully designed catwalk will allow for safe and quick performance of all inspection, maintenance, and service work. With the older straight tube bundle designs, there must be sufficient space to allow the bundle to come out of the housing, and safely lowered to the ground before installing the replacement – while tube bundle replacements aren’t usually needed very often, the replacement can be a multi-day process if allowances aren’t made for safe and efficient replacement. The older linear tube designs are slowly being replaced by the modular designs. With the modular design, the cooling bundles are removable from the side which is quick and performed safely in a few hours in the rare case of a cooling bundle getting worn to the point where it leaks. It is a simple matter to disconnect the incoming and outgoing water pipes; remove the mount bolts and replace. If there isn’t time to replace them, it is also a simple matter to bypass a given module until there is sufficient time to replace the cooling bundle after hours or off shift. The modular design uses a series of adjustable weirs which force the sand into a tortuous path to get through the body of the heater/cooler – this allows for much more accurate temperature control than the older straight tube design CAPITAL AND POWER REQUIREMENTS Depending on flow rate, incoming sand temperature, and desired set-point, a water-pipe design unit will cost twice as much as an electric-resistance design, with the very real potential to be three to four times as expensive once the installation costs are included. Depending on local utility standards, the demand charge simply for turning on an electric-resistance style heater for 30 minutes can be a large percentage of the monthly operating cost. If the foundry is not on a demand/time-of-day metering system this is not a problem, however most plants are on a demand-based system. Even a small, 300-lb/minute ER-style heater at 45 kW can be expensive to turn on and operate. If larger units for 1,000-3,000 lb./minute are used, running at 150-300 kW, the demand charges can be thousands of dollars even before the energy used is calculated. Because sand fluidization in an electric-resistance style system is accomplished with plant compressed-air, the cost of compressed-air must be included in the operation calculations. Depending on power costs and capital expenses, compressed- air can be reasonable to very expensive. A 300 lb./minute, 45- kW heater will use approximately 30-40 CFM at an incoming plant pressure of 90 psi. A 2,000-lb/ minute heater can use up to 150 CFM, depending on fluidization pressure. MAKING YOUR INSTALLATION ASUCCESS