US team advances “Super Boiler”

Des Plaines, Illinois — A US partnership between US research group Gas Technology Institute (GTI) and boiler maker Cleaver-Brooks has developed a new industrial steam-generation system to provide increased efficiency, reduced emissions, and lower fuel costs.

The gas-fired “Super Boiler” has a 40 to 50% smaller footprint and half the weight of conventional boilers, the developers claim . The design meets future nitrogen oxide (NOx) emissions regulations without the need for expensive post-combustion flue-gas treatments, GTI claims.

According to GTI, the unit is designed to achieve fuel-to-steam efficiency greater than 94% (HHV) while maintaining NOx and CO levels below 5ppm. Energy efficiency for gas-fired boilers is typically in the 75-83% range, and uncontrolled NOx emissions are about 70 ppm.

The Super Boiler consists of two main parts: the boiler and the heat recovery system. The boiler employs a split-combustion section for low-emissions, along with enhanced heat transfer innovations from Cleaver-Brooks, to achieve a very compact design.

The heat recovery system can recover most of the remaining heat in the flue gas from the boiler, including the “latent” heat associated with water vapor, explains Rick Knight, GTI R&D manager, power generation. This, he notes, accounts for two-thirds of the waste heat from natural gas combustion.

Two ultra-compact, high-efficiency economizers are incorporated into the system to recover sensible heat of the total flue-gas stream before it enters the TMC. In that device, water vapor passes selectively through a nanoporous ceramic membrane, giving up additional sensible heat and all of its latent heat to the boiler feed water.

A humidifying air heater (HAH) plays a critical role in managing water temperatures in applications that return and re-use a major portion of the condensate from their steam system. The HAH also conditions the incoming combustion air to further reduce NOx emissions in the boiler.

Laboratory tests have confirmed that the first 300-horsepower field-demonstration unit can achieve greater than 94% fuel-to-steam efficiency, said Knight, who estimates that this will save a facility over $50,000 annually in fuel, based on $12 per million Btu.

The Super Boiler is currently being trialled at Specification Rubber Products in Alabama, with a second pilot planned for later this year at a juice bottling plant in Ontario, California, according to GTI.