Large Commercial/Industrial Boilers
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Introduction
The U.S. manufacturing economy depends on over 54,000 large boilers to produce steam for process use, for heating and absorption cooling, to drive mechanical equipment (e.g., pumps and fans) and to generate electricity. It costs U.S. industry approximately $21 billion (1995 dollars) a year to feed these boilers. Total demand for steam is projected to increase 20% in five major industries by 2015 (from 1990 levels), with demand in food processing and chemicals being even greater. Industrial requirements for steam are increasing most rapidly in rubber, plastics, industrial machinery and transportation equipment manufacturing.
Fuel reduction can save enough money to recover costs within two years and in some cases immediately. According to the U.S. Department of Energy (DOE), a typical facility can realize savings of 20% by making routine maintenance and equipment and system improvements to their boiler systems, which translates to savings of $3,000 to $600,000 a year, depending on the size and type of the boiler system.
Technology Options
There are two general guidelines for improving the energy performance of existing boiler systems:
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There is a broad array of options in boiler equipment and controls that can enhance energy performance:
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Simple measures to improve efficiency include adding insulation where appropriate and installing proper, working steam traps.
Several diagnostic and preventive procedures are important to maintaining efficient operation. Flue gas temperature monitoring is useful in detecting efficiency and operation problems. Maintaining steady excess air levels (with an oxygen "trim" system) ensures that burners mix air and fuel efficiently. The Boiler Efficiency Institute provides maintenance and operation manuals for boilers and boiler controls. Low water levels can damage boiler vessels, so water levels must be checked frequently. Water treatment prolongs the life of boilers, while increasing efficiency. Waterside and fireside surfaces should be cleaned annually. Steam boilers should be blown down daily to remove sludge and sediment.
Routine maintenance of the entire boiler system should be performed at least annually, and often results in a 5% to 10% improvement in efficiency.
Efficiency Benefits
With proper maintenance, boiler life is indefinite. In most cases, it will outlive the process for which it originally was designed. Small improvements in a boiler’s efficiency can have a substantial impact on your energy costs, as illustrated by the 2 to 5% efficiency improvements in the table below.
Boiler Cost-Effectiveness Example | |||
(5,000,000 Btu/h Gas-fired Water Boiler) | |||
Performance | Base Model | Recommended Level | Best Available |
Thermal Efficiency (Et) | 78.0% | 80.0% | 83.2% |
Annual Energy Use (therms) | 96,200 | 93,700 | 90,100 |
Annual Energy Cost | $38,500 | $37,500 | $36,100 |
Lifetime Energy Cost | $654,000 | $638,000 | $613,000 |
Lifetime Energy Cost Savings | - | $16,000 | $41,000 |
Manufacturers
Manufacturers of commercial and industrial boilers and equipment include:
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Thomas Register publishes Boilers EZ Search, a directory of nearly 150 boiler manufacturers.
The American Boiler Manufacturers Association features a buyer's guide.
An industrial boilers manufacturers directory can be found at Industrial Quick Search Inc.
Purchasing Tips
Sizing and selecting a boiler system properly requires knowledge of your peak heating load and load profile. If building loads are highly variable, as is common in commercial buildings and industrial settings, designers should consider installing multiple modular boilers. Modular systems are more efficient because they allow each boiler to operate at or close to full rated load most of the time, with reduced standby losses. Other efficient options for handling variable loads are modulating boilers, which can run at partial capacity (instead of cycling on and off) and condensing boilers. While high-efficiency boilers are available for both water and steam models, water boilers and distribution systems tend to have lower maintenance requirements.
New units are purchased with a guaranteed efficiency at a Maximum Continuous Rating (MCR) for a specific fuel, producing a specified quantity of steam or hot water, at a specified temperature and pressure. Any changes in these characteristics shift the operating efficiency. Either the lower heating value (LHV) or higher heating value (HHV) should be used when specifying boiler efficiency. The gas flow decreases at lower loads, and with the same surface area, a larger decrease in gas temperature occurs. A 40°F decrease in stack gas temperature is equivalent to about a 1% improvement in efficiency.
DOE's Federal Emergency Management Program (FEMP) recommends selecting only boilers rated under the certification program run by the Hydronics Institute of the Gas Appliances Manufacturers Association (GAMA).
DOE's Energy Cost Calculator for Commercial Boilers can help you make informed boiler selection decisions.
Emerging Technology
Artificial intelligence (AI) has the potential to help optimize boiler operation reducing emissions, minimizing unburned carbon and maximizing overall efficiency. The Generic NOx Control Intelligent System (GNOCISTM) is an AI program developed to provide process control that achieves NOx reduction consistent with economic and operational constraints.