Document e1mrdLRnXga94b22xpaX9Or2M

390 CHAPTER IS 1958 Guide For burning rates from 100 to 1200 lb coal per hour - where H = 0.03 B + 24 /'' H = minimum setting height, inches, measured from dead plates to crown.sheet for steel boilers. For cast-iron boilers height may. be i H. B = burning rate coal per hour, pounds. Standards for minimum firebox dimensions and base heights have been formulated by the Stoker Manufacturers Association as shown in Fig. 11.* In considering these recommendations, it should be understood that they show the average recommended minimum. There are many factors affecting the proper application of stokers to various types of boilers and furnaces, and, in certain instances, setting height or firebox dimensions shown in the standards may be modified without impairing performance. Such modification will depend upon the experience of the installer or de- Automatic Fuel Burning Equipment 391 or hot water heating system, a piping and pick-up factor of 1.33 is com monly used in sizing the stoker, but this factor should be increased at times due to unusual conditions. Controls The heat delivery from the stoker of the smallest household type to the largest industrial unit can be regulated accurately with fully automatic controls. The smaller heating applications are controlled normally by a thermostat placed in the building to be heated. Limit controls are supplied to prevent excessive temperature or pressure from being developed in the furnace or boiler, and refueling controls are used to maintain ignition during periods of low heat demand. Automatic low water cut-outs are recom mended for use with all automatically-fired steam boilers. (See Chapter 38.) DOMESTIC OIL BURNERS An oil burner is a mechanical device for producing heat automatically from liquid fuels. Two methods are employed for the preparation of the Fig. 11. Suggested Minimum Firebox Dimensions and Base Heights* * For reference in selecting or designing boilers and furnaces for stoker firing. Dimensions shown are for net inside clearance at grate level using coal with heating value of not less than 12,000 Btu per pound. Under certain conditions smaller fireboxes will permit satisfactory performance but these dimensions are preferred normal minimum^. signer with a particular stoker, the type of fuel used, and the construction of the boiler or furnace. . Installation of stokers (particularly smaller sizes) on the side of the boiler or furnace will sometimes facilitate clinker removal. Rating and Sizing Stokers The capacity or rating of small underfeed stokers is usually stated as the burning rate in pounds of coal per hour. Codes for establishing uni form methods of rating anthracite and bituminous coal stokers have been adopted by the Stoker Manufacturers Association.1 The Association also has adopted a uniform method of selecting stokers that is published in convenient tables and charts.* The required capacity of the stoker is calculated as follows: .Load (Btu per hour) Stoker burning rate = required (pounds of Heating value of coal (Btu per pound) X overall efficiency of stoker and boiler or furnace coal per hour) In determining the total load placed on a stoker-fired boiler by a steam Fig. 12. High-Pressure Atomizing Oil Burner oil for the combustion process; atomization, and vaporization. The simpler types of burners depend upon the natural chimney draft for supplying the air for combustion. Other burners provide mechanical air supply or a combination of atmospheric, and mechanical. Ignition is accomplished by an electrical spark or hot wire, or by an oil or gas pilot. Some burners utilize a combination of these methods. Continuously operating burners may use manual ignition. Burners of different types operate with lumi nous or non-luminous flame. Operation may be intermittent, continuous with high-low flame, or continuous with graduated flame. Classification of Burners . Domestic oil burners may be classified by type of design or operation into the following groups: pressure atomizing or gun, rotary, and vaporlzing or pot. These are further classified as mechanical draft, and natural draft. Pressure Atomizing (Gun Type) Burner TiP1111 burners are usually designed to bum No. 1 or 2 grade fuel oil. `ney may be divided into two classes: high-pressure and low-pressure