Operating of a boiler

Combustion. Most of the mined coal is burned to produce steam for electric power generation (qv). The calorific value determines the amount of steam that can be generated. However, the design and operation of a boiler requires consideration of a number of other properties (see Furnaces, FUEL-FIRED). 

The opposite scenario also may occur, whereby a localized pre-boiler water chemistry problem can affect the downstream, mechanical operation of a boiler. As an example, difficulties in the control of pretreatment equipment may lead to treated MU water instability, causing downstream after-precipitation, leading to FW line blockages, and finally resulting in boiler cutout as a result of low water. 

The use of FW that has been inadequately pretreated makes the mechanical operation of a boiler and the control of boiler water conditions innecessarily difficult. Additional quantities of internal treatment chemicals and higher rates of blowdown (BD) are usually required, which reduces boiler plant efficiency and raises the cost of generating steam. 

A book into which all notable events, problems, and requirements identified during the operation of a boiler are recorded. 

The relationship between temperature and pressure holds true only in the presence of pure steam adulteration with air contributes to a partial pressure but not to the temperature of the steam. Thus, in the presence of air the temperature achieved will reflect the contribution made by the steam and will be lower than that normally attributed to the total pressure recorded. Addition of further steam will raise the temperature but residual air surrounding articles may delay heat penetration or, if a large amount of air is present, it may collect at the bottom of the sterilizer, completely altering the temperature profile of the sterilizer chamber. It is for these reasons that efficient air removal is a major aim in the design and operation of a boiler-fed steam sterilizer. 

Another example of optimization can be encountered in the operation of a boiler. Engineers focus attention on utilities and powerhouse operations within refineries and... 

Boiler losses can be plotted as a function of excess air (top). The minimum of the total loss curve of a boiler is the point where optimized operation is maintained (bottom). Most efficient operation of a boiler occurs when the amount of excess air in the stack balances the losses of unburned fuel. 

A number of hazards are associated with the operation of a boiler system. Some of these hazards include ... 

To understand the operation of a boiler, it is necessary to observe what happens from input to output of the unit. Several cycles are involved in the complete operation of the unit. The heat cycle, the water and steam cycle, and the boiler-water circulation cycle all interact to produce the output of the boiler. Fuel and water are brought to the unit water is heated to its final predesignated condition (water and/or steam) and transported to the point of its end use. When the heat has been taken out of the water, the remaining steam and water mixture (or condensate), if usable, is returned to the unit and recycled. 

Water treatment is required for satisfactory operation of a boiler at the initial start-up to prevent any deposition of scale and to prevent any corrosion from acids, oxygen, and other harmful substances that may be in the water supply. A qualified water-treatment specialist should be consulted and the water should be appropriately treated. 

I. P. Epik, Effect of the Mineral Part of Shales on the Conditions of Operation of a Boiler Plant, Estgosizdat (1961). 

M. Bashar and T. S. C2amecki, "Design and Operation of a Lignite-Fired CFB Boiler Plant," Proceedings of the Tenth International Conference on Fluidi d Bed Combustion, San Francisco, May 1—4,1989. 

A difference between these firing methods may also be manifested in the initial fuel cost. For efficient operation of a spreader-stoker-fired boiler, the coal must consist of a proper mixture of coarse and fine particles. Normally, double-screened coal is purchased because less expensive run-of-mine coal does not provide the optimum balance oFcoarse and fine material. 

Vessels, e g., waste heat boilers, in which steam is generated incidental to the operation of a processing system containing a number of pressure vessels, such as are used in chemical and petroleum products manufacture. (Equipment which may fire a supplemental fuel should be considered as a fired pressure vessel.)... 

NOTE Aclress h) i. required only in the case of a boiler used on a temporary location, e.q.. on a building operation, work of engineering construction. 

In order to monitor the safe operation of the boiler a daily and weekly program of tests should be drawn up and log sheets completed as verification of the tests being carried out. Items checked should include ... 

Electrode boilers produce hot water or steam (generally saturated steam) by conducting current through the BW. The water provides resistance, which causes heat to be generated when electrical current flows from one electrode to another. As a consequence, the electrical conductivity of the water is a primary factor in the satisfactory operation of these boilers. Other aspects of water treatment control (such as alkalinity levels, oxygen content, and foam control) and maintenance also must be considered if optimum efficiency is to be obtained. 

Water treatment monitoring and control is often a knife-edge operation and must be tailored to the overall operation of the boiler because waterside and gas-side problems usually are interlinked. Consequently (and as with other types of WT boiler), not only should the utility boiler FW be essentially free of dissolved oxygen to prevent waterside pitting corrosion of the economizer and other boiler components, but also the temperature must be high enough to prevent dewpoint condensation and subsequent acid attack on the gas side of the economizer tubes. 

Operators of smaller boiler plants, on the other hand, usually open the boiler sampling coil only when it is necessary to take a water sample. In this case, the BW should be allowed to run for several minutes before the sample is taken. 

Clearly, therefore, the design and correct utilization of the FW tank and associated FW equipment is of paramount importance in ensuring the continuous, efficient, and smooth operation of the boiler plant system. As an aid to design, a schematic drawing of a FW tank indicating some of the important elements is shown in Figure 3.5. 

For smaller facilities this is not always the case, and many boiler houses will not necessarily require the presence of permanent operators, which can sometimes make the smooth implementation and seamless operation of a water treatment program quite difficult to achieve. 

To achieve this objective at the operational level, consistently good water treatment practice is required on site. However, achieving this objective cannot and should not be the sole prerogative or responsibility of any one person. Rather, if success is to be attained and maintained, it requires a proactive approach with joint participation, support, and communication by the water treatment service company and the owners and/or operators of the boiler plant. 

The steam system cycle is a regenerative water heating, steam generation and delivery, and condensed steam recovery cycle. It involves the operation and management of a boiler(s) and some or all of the auxiliaries and balance of plant equipment discussed in Chapters 2 and 3. 

A further example is the effect of tube failure resulting from longterm overheating. Here it is likely that the principle contributing causes are a combination of deposit formation and stresses resulting from mechanical operation of the boiler in excess of design limits. To minimize or eliminate the risks of deposits and the subsequent effects they produce within the boiler, control again requires a twofold approach ... 

The corrosion of steel and other metals in a boiler system takes place when an electrochemical cell is established, although the rates of corrosion and the types of corrosion mechanisms involved are highly dependent on the particular circumstances that develop during the operation of individual boiler plants. A failure to adequately control corrosion ultimately leads to the failure of boiler surface components or other components and items of equipment in the system. 

It is generally agreed that the causes and effects of poor water chemistry, mechanical problems, boiler section corrosion, metal failure, and poor boiler plant operation are all closely interrelated. Thus, effective control over the various corrosion processes that may occur in a boiler and its auxiliary equipment is fundamental to the realization of the full life expectancy and safe operation of the plant. Corroded and wasted metal cannot be replaced easily, and the failure of a boiler in service is both potentially dangerous and expensive. 

This use of soda ash as a reactant for FW contaminants is much rarer today than, say, 25 or 30 years ago simply because the steam-water space design and high heat-flux operation of modem boilers cannot tolerate the volumes of carbonate and hydroxide sludges produced. 

The use of CHZ as a passivator to reduce crud levels and minimize the associated problems has proved to be particularly beneficial in powergenerating boilers. For other types of operations, however, involving the continuous operation of industrial boilers with much longer steam and condensate line systems, the benefits of CHZ are not so dramatic and the material is seldom the product of choice for nonutility applications. 

In general, the tables simply provide recommendations for the operational control of FW and BW chemistry and are not designed to be a set of inflexible rules. Consequently, if experience confirms that alternative program control limits will lead to safer, easier, and more reliable operation of the boiler plant, then experience should be the deciding factor. 

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