Boiler performance

NOTE Soot blowers are typically employed only on WT boilers and may be regarded as appurtenances because boiler safety and reliability is directly related to the cleanliness of the heat transfer surfaces. Boiler performance and efficiency also depend on the same heat-transfer cleanliness factors. 

The steam purity limit represents an achievable level if other tabulated water quality values are maintained. ASME points out that the limit is not intended to be, nor should it be construed to represent, a boiler performance guarantee. 

Boiler performance is determined by the conductivity of the BW. The optimum conductivity range is dependent on the specific boiler design. 

The efficiency of boilers changes with the boiler load. The variation of boiler performance with load can be approximated by4 ... 

Figure 23.6 Steam boiler performance at part-load.

Waterwall furnaces were employed by the ancient Greeks and Romans for household services. A water boiler, found in Pompeii, was constmcted of cast bronze and incorporated the water-tube principle (2). The earliest recorded instance of boilers performing mechanical work (130 bc) was Hero s engine... 

Many mills bum this wood waste in boilers to obtain heat energy for process steam, and to alleviate possible solid waste disposal problems. These waste wood boilers are known as "hog-fuel" boilers. A base load of supplemental fuel of some kind is required in hog-fuel boilers, because the significant variations of the size, moisture content, and heating value of the wood waste may not allow consistent boiler performance. Supplemental fuel facilitates uniform boiler combustion, and ensures that a minimum amount of power is generated regardless of the fuel value of the wood waste at any one time. 

A positive result of TDF use in waste wood boilers is that facilities are able to bum sludge and waste wood more successfully, decreasing the likelihood of solid waste disposal problems. Results from a series of waste wood boiler performance tests using ASMS codes concluded that use of TDF supplementally in hog-fuel boilers enhances combustion of wood waste, and enables disposal of biological sludge in conjunction with wood waste without necessitating use of other fossil fuels such as coal.2 No applicable environmental limits were exceeded during these tests.2... 

The project at Plant Sweatt was organized with Southern Company Services as EPRI s prime contractor responsible for project management, project direction and subcontractor performance. Subcontracted to Southern Company Services were Babcock Wilcox (B W) and KVB. B W provided technical consultation and boiler performance evaluations, KVB provided combustion gas emission characterizations and supplementary technical consultation. 

During the longevity testing on the last three fuels, data acquisition was done manually and with less frequency due to constraints 1n funding and available manpower. Boiler efficiency calculations for the longevity tests were done on the SCS Boiler Performance Code (BPC) after BPC results were validated against the B W Computerized Boiler Diagnostic System. No data on particulates were taken on these last three fuels for the reason stated above. 

Sometimes the opposite is also the case, that is, the boiler itself restricts the type of flue gas treatment system that can be installed. Most electric power generating facilities have coal specifications required by the boiler design and the manufacturer s warranty. These sulfur and ash specifications are designed to optimize boiler performance and avoid fatigue of boiler materials. Boiler design and coal specifications can limit the type of system that can be applied. The construction date of a boiler determines the level of pollutant control required, and it also goes far toward determining the type of flue gas treatment system that can achieve this level of emissions control. 

Bakker, R. R., Jenkins, B. M., Williams, R. B., Carlson, W., Duffy, J., Baxter, L. L., Tiangco, V. M. (1997), Boiler Performance and Furnace Deposition During a Full Scale Test With Leached Biomass. Proceedings 3 Biomass Conference of the Americas, Montreal, p.497. 

Combustion tests were conducted at the Bay Front Unit No. 3 of Northern States Power Co. in Ashland, WI, The coal-fired underfeed stoker with boiler rated at 45,400 kg/h steam at 5.1 MPa drum pressure and 455 C was modified to receive 4.6 m long whole tree sections from a charge chamber by means of a ram feeder. A higher pressure over-fire air system was added. The tests successfully demonstrated the feasibility of replacing coal with logs on a grate without a loss in boiler performance. 

The boiler efficiency and some data for a boiler are outlined in Problem 4.140. Depada-tion of performance and economic loss result from poor boiler performance. What are some of the steps you might take to improve boiler performance ... 

In contrast to the silicates, most carbonate and many sulfate minerals dissolve exothermically (AW ° < 0). This makes them most soluble at low temperatures and gives them a tendency to precipitate as temperature increases (Fig. 1.7). (Compare log versus /T curves for calcite and quartz in Fig. 1,7.) Thus, calcite (AW° = -2.30 kcal/mol) can be a troublesome precipitate on the walls of boiler systems where its thermal insulating properties prevent heat exchange and can seriously damage boiler performance. 

Whenever test results are assessed and used to establish boiler design parameters, the representativeness of the test sample must be carefully considered. The degree of variability in the coal deposit and the impact of this variability on boiler performance must be evaluated. Judgements are also required on the effects of more gradual changes that could occur in coal properties as a function of time and location in the coal seam. 

Richter, W. and Pohl, J. H., "Scale-Up of coal Water fuels Experiments In Pilot Furnaces For Evaluation of Utility Boiler Performance, 7th Int. Symp. on Coal Slurry Fuels Preparation and Utilization, New Orleans Louisiana, May, 1985. 

Complex-wide the current scope of monitoring is to weekly calculate all heat exchanger/boiler performance, catalyst activity, compressor/turbine... 

In order to obtain a complete picture of the boiler performance several types of efficiency tests need to be conducted. The main test is a so-called combustion efficiency test. For a better picture, it may be combined with one or more specialized tests such as carbon monoxide testing, hydrogen testing, and others. 

Another boiler performance parameter is "thermal efficiency." Thermal efficiency characterizes the heat exchange effectiveness and measures the ability of the heat exchanger(s) to transfer heat from the combustion product to the water or steam in the boiler. However, thermal efficiency does not account for radiation and convection losses due to boiler body design specifics or other components, so it cannot be considered a true boiler efficiency for economic evaluations. 

It appears that for a specific fuel (HHV) and a specific fuel flow (thf) boiler performances are effected by three contributions ... 

When a boiler is set up in field the mentioned parameters like chimney losses, envelope losses, and electrical consumption affect boiler performances in different ways based on ambient conditions. Figure 34.15 shows the components that interact with the boiler the hydraulic piping, the heating elements, and the control system. A correct matching between boiler and these systems plays an important role in the building s energy performances and the real efficiency of boilers is closely linked to them. It is reported [1] that "less than 50% of the overall efficiency is due to the quality of the boiler."... 

Poor boiler performance because of accretions and fouling... 

The ultimate analysis is used with the heating value of the coal to perform combustion calculations including the determination of coal feed rates, combustion air requirements, weight of products of combustion to determine fan sizes, boiler performance, and sulfur emissions. 

The self-heating of coal is due to a number of complex exothermic reactions. Coal will continue to self-heat provided that there is a continuous air supply and the heat produced is not dissipated. The property of coal to self-heat is determined by many factors, which can be divided into two main types properties of the coal (intrinsic factors) and environment/storage conditions (extrinsic factors). Self-heating results in degradation of the coal by changing its physical and chemical characteristics, factors that can seriously affect boiler performance. 

Benchmarking the fuel cost for steam generation is an important step in managing the steam system. For a given amount of steam production, the total fuel cost depends on boiler efficiency, steam pressure, fuel type and cost, and feedwater temperature. The benchmark can serve as a tracking tool for monitoring the boiler performance. The benchmark calculations are provided (DOE, 2012), which are briefly illustrated next. 

The economic considerations associated with using opportunity fuels have been well identified by Letheby [4, 5] and Williams [32]. These issues extend beyond the cost of the fuel in /GJ ( /10 Btu). Among the economic issues is fuel transportation cost. Many opportunity fuels must be located near the power plant or energy user, due to inordinate impacts of transportation on final fuel costs. In addition, economic impacts include the monetary consequences of using the fuel with respect to boiler performance capacity, efficiency, and operability. They also include the impact of the fuel on emissions and emissions credits reductions in SO2 and NO emissions currently have significant economic values in the US. 

Table 10-11 indicates projects intended to demonstrate some of these combustion modification technologies for commercial feasibility or demonstrate applicability where they have not been used previously. The degree of NO, reduction achievable while maintaining acceptable boiler performance is an important element of these test programs. As of mid-1994, all of the programs had been completed except the TVA micronized coal rebuming program. 

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