The Case for Utility Boiler Fuel Delivery System Upgrades

A vital part of any coal-fired unit is its fuel delivery system (FDS). A newly formed subcommittee of the ASME Research Committee on Energy, Environment, and Waste has investigated potential FDS upgrades on three typical 500-MW wall-, tangential-, and cyclone-fired boilers. The subcommittee has produced a series of suggested upgrades that have a simple payback of no more than two years.

The American Society of Mechanical Engineers’ Research Committee on Energy, Environment, and Waste (RC EEW) was formed more than 40 years ago with a focus on industrial and municipal solid waste. The Fuel Delivery System Subcommittee was recently formed to expand the RC EEW’s original charter to include all fuels, including the energy and environmental aspects of those fuels. The first project undertaken by this subcommittee, begun in September 2011, was a feasibility and economic analysis of potential upgrades to Powder River Basin (PRB) coal-fired power plants. A summary of results of the subcommittee’s work to date follows.

The first step in the subcommittee’s analysis of fuel delivery systems (FDS) was to identify the family of plants of interest. A recent article (“Predicting U.S. Coal Plant Retirements,” May 2011, available in the POWER archives at powermag.com) noted that the U.S. coal-fired fleet consisted of 1,105 units with a total nameplate capacity of 342 GW at the time the article was published. A majority of those plants were between 20 and 85 years old; only 35 new plants had been added over the past 15 years.

As a group, the units 50 years and older constitute about 53 GW or 20% of the total fleet capacity and 40% of all coal-fired units—many of which may be retired due to either normal business decisions or the cost of mandated retrofits of new air quality control systems (AQCSs). The next age group, the 30- to 45-year-old units, represent 216 GW and 63% of the current coal-fired fleet. Many of these were built during the 1960s and are much more likely to invite investment in plant upgrades (Figure 1).

1. Coal fleet average unit nameplate rating. The average unit rating was calculated by averaging the rating all of the units within each age category. Data are from early 2011. Source: POWER and Burns & McDonnell

The boilers of the 30- to 45-year-old units are mainly of opposed wall-, cyclone-, and tangential-fired configuration with average capacity factors ranging from 61.8% to 73.3%, as shown in Figure 2. In this age group, there were about 226 opposed wall-fired, 143 tangential-fired, and about 15 cyclone-fired boilers in operation in the U.S. in 2011.

2. Coal fleet average capacity factor. The average unit capacity factor was calculated by averaging the reported capacity factor of all the units within each age category. Many of the units in the five years or less category did not have data available. A 75% capacity factor was estimated. In all categories, if capacity factor data was not available, that unit was omitted from the average. Data are from early 2011. Source: POWER and Burns & McDonnell

These units—the backbone of the baseload coal-fired fleet—will bear the burden of ensuring that the usual high standards of electrical grid performance, availability, and reliability are met in the future. Though most of these units have high-grade AQCSs, they will require upgrades to comply with maximum achievable control technology, but the cost is not forecast to adversely impact unit competitiveness in terms of generation cost. However, the additional AQCS upgrades required for environmental compliance will add additional complexity to plants now straining to maintain unit availability and capacity factor.

A vital part of any coal-fired unit is its fuel delivery system, as shown in Figure 3. For the purposes of the subcommittee’s analysis, the FDS consists of the feeders, pulverizers (mills), classifiers, coal piping, and burners. These systems are vital for efficient and reliable plant operations but also require substantial maintenance due to the abrasive nature of coal.

Table 1. A comparison of possible fuel delivery system upgrades and their benefits. Source: The Fuel Delivery Subcommittee of the ASME Research Committee on Energy, Environment, and Waste

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