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Field-Erected Boilers

Utility boilers are large field-erected, high-pressure/high-temperature boilers with relatively uniform design and similar fuel combustion technologies. They can be fuelled by pulverized coal, No. 6 oil or natural gas. Shipping and handling costs for a very large and heavy packaged boiler can be very expensive to certain parts of the country. When such costs are compared to the cost of field erecting a boiler, it is often a better economic as well as technical decision to purchase the boiler for complete or partial field erection.

Large watertube boilers used in industries and utilities with large steam demands are normally assembled and constructed in the field. Large boilers operating at a steam pressure in excess of 800 psig are good candidates for total or modular field erection for another reason. As the operating pressure exceeds 800 psig, the specific volumes of the steam and water converge dramatically. For example, the ratio of the specific volumes of steam to water for a boiler operating at 150 psig is 152. This same ratio for a boiler operating at 900 psig is only 23. Effective operation of natural circulation boilers depends upon this ratio. Circulation can be improved by increasing the height distance between the steam and lower drums and the headers. This can be achieved through complete or modular field erection.

The bottom line: When purchasing a boiler that will operate above 175,000 PPH steam temperatures and pressures, thoroughly assess and compare the design, operating cost and shipping considerations of packaged vs. field-erected units.

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