When to use electric steam boilers?
Packaged electric boilers, in the right applications, are an effective way to offset rising fuel prices and help maintain profitability. They can also serve as a backup should an unforseen shutdown of the main plant boiler occur.
Key concepts
- • Electric steam boilers can supply process needs when large central boilers are shutdown
- • When central boiler turndowns are too high, electric boilers are economical to operate
- • Electric boilers can deliver steam in one-half hour
- • Fossil fuel producers are again turning up the heat on industrial and commercial operators of large fossil-fueled steam boilers. Since there is little boiler operators can do to control energy costs, the obvious answer is to find ways to control consumption — without curtailing operations or compromising the productivity of steam-heated processes.
- • Fortunately, as the weather warms, reduced demand for space heating allows large central boilers to be turned down. But this still leaves operators literally “blowing off steam” when the same boiler provides steam for processes. Typically, even at the maximum turndown ratio, a boiler produces more steam than processes need, and this excess is vented to the atmosphere. The wasted energy represents a significant fuel cost on the input side.
- • A packaged electric steam boiler may be a more economical solution. It can keep steam-consuming operations running at full speed, while the big fossil-fueled boiler takes the summer off or has to be maintained or repaired.
What about electricity costs?
Although electric utilities are some of the largest operators of fossil-fueled steam boilers, they suffer less from rising oil and gas prices because of coal usage. Those that use oil and gas have more clout with suppliers because of their size and usage volume. Most industrial and commercial boiler operators probably pay a premium for electric energy compared to oil and gas for equivalent Btu quantities. A total-cost comparison points out the advantages of using an electric steam boiler to generate process steam when overall plant steam requirements are reduced.
Applications
Packaged electric steam boilers are available to produce low and high-pressure steam at rates up to at least 165 BHP. Some manufacturers will custom build larger electric boilers for specific installation requirements. Electric boilers are suitable for a wide range of processes, including those used in the manufacture of chemicals, paints, paper, textiles, petroleum products, pharmaceuticals, plastics and rubber; as well as food and beverage processing and many other facilities where heat, humidification, and sterilization are required.
Specific applications include supplying steam for storage tanks and jacketed vessels; reaction and distillation vessels, retorts, and autoclaves; heat rolls for paper coating, calendaring, laminating, corrugating and embossing; platens, dies and molds used in the processing of plastics and elastomers
Although the main plant boiler usually supplies steam and hot water for comfort heating and humidification, there may be cases where it is cost effective to install an electric boiler for localized heating in a plant expansion. Similarly, electric boilers are ideal choices for new process facilities where large, fossil-fueled boilers are impractical or not required. With a properly sized electric boiler, there are no onsite combustion stack losses, stacks, or stack emissions. Compared to oil fired boilers, there are no fuel storage tanks to install, keep filled or worry about leaking. Also, there is no maintenance required for burners and heat exchanger surfaces.
Packaged electric boilers are delivered with all controls and ordered accessories in place and ready to operate. Custodial personnel with a minimum of training can operate most electric boilers. They start quickly, delivering steam within one-half hour. They are safe, compact, quiet-running units that can be installed close to the site of steam consumption, eliminating the need for long pipe runs and pipe heat losses that can run as high as 10%. Electric boilers are well insulated, so they don’t add significant heat to the surrounding area. They operate on existing distribution voltages and the only additional requirement is a feed water supply.
Maintenance on electric boilers is minimal beyond routine inspections of water levels and monthly inspections of wiring. As with all boilers, they do require scale control measures and periodic blowdowns to maintain efficiency. Heating element replacement, when required, is easily accomplished through the boiler door.
Sizing and selection
Since packaged electric steam boilers are pre-engineered and assembled, and installation requirements are similar for most units, sizing and selection from a list of standard products generally is a straightforward process. Most heating applications involve only four steps to determine the correct BTU capacity of the boiler.
- 1. Determine the number of BTU/hr required to bring the application up to the operating temperature in the desired time, including piping.
- 2. Determine the number of BTU/hr required to maintain the operating temperature in the process and the piping.
- 3. Taking the largest result from Step 1 or Step 2, convert the BTU/hr into pounds of steam per hour, using standard saturated steam data . Divide the BTU/hr required by the latent heat in Btu/lb at the process working or gauge pressure.
- 4. Convert the pounds of steam per hour into the boiler kW requirements. Since saturated steam tables are based on feed water at 32 deg F, a simplified kilowatts-per-pound-of-steam table is used to determine a correction factor for feed water at some higher temperature. Multiply the required pounds of steam per hour from Step 3. by this correction factor.
