Tham khảo tài liệu 'central boiler plants episode 1 part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | TM 5-650 SECTION III. PRINCIPLES OF STEAM AND HOT WATER GENERATION 1-14. BASIC PRINCIPLES The generation of steam occurs as a result of two separate processes combustion the release of heat by burning fuel and heat transfer the absorption of heat into the water. Combustion was discussed in the previous section. A study of the heat transfer process can be made with an elementary boiler as shown in figure 1-7. The boiler system can be represented as a container equipped with an outlet pipe and valve a pressure gage and a thermometer immersed in the water. If a fire is built under the unit and water at 32 F is put into the container with the valve left open the water temperature will rise steadily as the fire burns until a temperature of approximately 212 F is reached. At this time the temperature will rise no further but the water will gradually boil off and if firing is continued long enough all the water will be evaporated. If the heat content of the fuel source is accurately measured it can be demonstrated that to raise the temperature from 32 F to the boiling point the heat input was 180 Btu for each pound of water. It would also be shown that 970 additional Btu for each pound of water is required to boil off all the water. This additional heat is called the latent heat of vaporization and represents the heat required to convert the small volume of liquid into a large volume of steam. With the valve in a closed position and using another batch of water repeat the process and allow pressure to build up to 100 psig then throttle the valve so that pressure is maintained at 100 psig. The temperature in the container will now be approximately 338 E This is called the saturation temperature for 100 psig pressure. The heat input required to raise one pound of water from 32 F up to this saturation temperature is 309 Btu. The energy expended in boiling one pound of water from 338 F at 100 psig is Btu. The temperature required to boil the water increases as the .
