Boilers are pervasive in energy-intensive industries and critical to successful plant operations. Active management of steam quality, steam purity, carryover, corrosion, scale, and energy consumption is necessary to extend a boiler’s useful life and improve its efficiency.
Proper control of the boiler water reduces carryover, corrosion, and scale. “Our level control systems can accurately control water levels and can be configured to best suit the actual system in place,” says Andy Butcher, product manager for Spirax Sarco (www.spirax.com). “The systems can provide additional alarms, trending, and even remote monitoring with digital communications. On-off control can be provided where the feedwater valve or pump is switched on or off when the level deviates from a preset band, or, for even better accuracy and reduction of the likelihood of carryover, modulating control can be provided.”
Spirax Sarco TDS (total dissolved solids) controls can continually monitor the amount of dissolved solids in the boiler water and adjust it with various surface blowdown schedules. “Our blowdown controllers can work alongside our level controllers and provide digital communications for remote monitoring,” says Butcher.
Some water management technologies are specifically designed to prevent corrosion. For example, the CA-6 Online Analyzer from Electro-Chemical Devices (www.ecdi.com) uses colorimetric technology to measure silica levels in boiler water, and the company’s Triton DO9 Dissolved Oxygen Analyzer with its potentiostatic three-electrode design allows continuous measurement of trace levels (ppb) of dissolved oxygen in boiler feed water.
Incomplete steam separation causes carryover, which affects process streams and product quality. “Plant design engineers need to work with the equipment manufacturers to select the most suitable steam separation equipment to effectively prevent severe steam contamination,” says D. Neil Bradwell, principal engineer for Indeck Keystone Energy (www.indeck-keystone.com).
Problems caused by carryover can be managed with specialized equipment. “Clayton Industries’ steam generators include as part of their design a mechanical fixed vane steam separator to assure our customers get dry steam,” says Nand Bogman, vice president of applications for Clayton Industries (www.claytonindustries.com). “We offer units with a guaranteed 99.5% quality steam output. Our competitors are normally are in the 98% quality range and have to use an external separator to match our numbers.”
With the right boiler and piping design, steam quality issues can be minimized. “Fulton offers packaged, pre-piped systems where our engineers will design the steam header based on required volumes of steam, velocity requirements, steam trap requirements, and system loads,” says Melissa Wadkinson, chief engineer at Fulton (www.fulton.com). “While there are engineering firms who design plant piping systems, very few boiler manufacturers will offer the packaged boiler skids including the main steam header and takeoffs to ancillary equipment, such as deaerators.”
Boilers are prime candidates for waste heat recovery. Cannon Boiler Works (www.cannonboilerworks.com) leverages U.S. Department of Energy-supported technology in its advanced high-efficiency heat recovery system. Cannon’s Ultramizer recovers sensible and latent heat, as well as water from the exhaust stream. The first two stages of the system use Cannon’s Feedwater Heater technology. In the Ultramizer’s third stage of heat and clean water recovery, a transport membrane condenser (TMC) system, patented by the Gas Technology Institute, is used. The TMC uses a nanoporous membrane to selectively remove pure water from natural gas combustion byproducts in order to boost fuel-to-steam efficiency. The Ultramizer combines the best aspects of direct-contact and indirect-contact condensing economizers, differentiating it from conventional condensing economizers.
“The Cannon Boiler Works Ultramizer is unique in the field of boiler heat recovery devices in that not only does it recover wasted sensible and latent heat, but returns clean, usable water to the boiler system, as well,” says Kari Savolainen, Ultramizer product manager. “The combined benefits of increased boiler efficiency, up to 95%, reduction of greenhouse gas emissions, and recovery of a previously untapped source of water for the boiler system should prove very attractive to those users who are looking not only to reduce operating costs, but improve their sustainability profile.”
The Ultramizer benefits existing and new boilers as well as non-boiler applications that have a hot and moist clean exhaust flow. Most often used on natural gas combustion products, it is also suitable for micro turbines, reciprocating engines, fuel cells, and steam vents. Cannon Boiler Works was granted exclusive commercial use to the TMC technology in 2009 and the Ultramizer was launched in 2011.