Preheating of boiler

The flue gas generated in the tubular reformer is used for preheat of reformer and prereformer feed, natural gas preheat, steam superheat and preheat of combustion air. The synthesis gas generated in the tubular reformer is cooled by high-pressure steam generation (4), preheat of boiler feed water and reboiling in the distillation section (5). 

The heat in the exit gas is recovered downstream the tubular reformer, usually by the production of steam, preheating of boiler feed water, etc. The final separation into the desired product compositions depends on the application. Pressure swing adsorption (PSA) is in most cases used if pure hydrogen is desired. Pure carbon monoxide can be obtained by cryogenic separation in a cold box. Adjustment of the H2/CO ratio can be accomplished by polymer membrane modules with different selectivities for permeation of the two compounds. 

Waste heat recovery by generation and/or superheating (especially in S-350 configuration) of high pressure steam and preheat of boiler feed water... 

Economizer. The economizer is a tubular heat exchanger used to recover heat from the exhaust gases from boilers or some processes. It is used in boilers to recover much of the sensible heat for use in preheating the boiler feedwater. An increase in boiler efficiency of 4-6 per cent is typical. The design and materials of construction depend on the application. 

Metal cleaning wastes include wastewater from chemical cleaning of boiler tubes, air preheater washwater, and boiler fireside washwater. 

Boiler feed Water Preheating By preheating 5413 kg/hr of boiler feed uater, required from 100 TPD sulphuric acid plant, to 68°C using part of thermal energy available in acid coolers, 312 kg/hr of additional steam can be generated. This results in an additional availability output of 0.287 x 10° K3/hr. By this,... 

The basic principle of the process, which is licensed by IFP SNAM (Societa Nazionale Metanodotii) etc., comprises preheating of the hydrocarbon feedstock and boiler feed-... 

To illustrate, in a fossil fuel power plant the loss of boiler air preheater(s) can create a sudden increase in flue gas temperature from <300°F up to 500°-700°F for a brief (e.g., 20-30 minute) period. (Air preheaters are energy conserving heat exchangers that heat incoming boiler combustion air with hot boiler flue gas which is thereby cooled prior to particulate scrubbing. If an air preheater fails, the hot flue gas will not be cooled by the heat transfer to the in-... 

Feedwater heaters are used to increase the efficiency of steam power plants. A particular heater is used to preheat 10 kg/s of boiler feed water from 20°C to 188°C at a pressure of 1200 kPa by mixing it with saturated steam bled from a turbine at 1200 kPa, as shown in Fig. P4.76. Although insulated, the heater loses heat at the rate of 50 J per gram of exiting mixture. What fraction of the exit stream is steam ... 

In the case of 65% moisture content, the adiabatic combustion temperature is so low that preheating of the combustion air would be necessary to ensure complete combustion. The combined influence of increased flue-gas volumes and decreased temperature level means that a larger and more expensive boiler is required when firing a fuel with higher moisture content. 

Developmental goals considered to be necessary for acceptable performance include a turndown ratio of 3 1 or better, minimum burner-tip life of 2000 h, air preheating of less than 150°C (300°F), maximum droplet size of 300 rm, and carbon conversion efficiencies of greater than 99%. Small-scale tests suggest that these coals are achievable, but what is yet required is long-term demonstration in large electric-utility-size boilers in the 100-500 MW range. 

Maximise heat recovery from aU possible sources. Use outgoing hot process streams for preheating of incoming cold process streams. (Outgoing depleted hot oleum stream at 125—130 °C from oleum boiler is used to preheat the incoming concentrated oleum stream at 50—55 °C into the oleum boiler by an oleum/oleum heat exchanger in a liquid SO3 plant). 

Demineralization of boiler water with calcium under optimum conditions can reduce the silica level to 0.4 ppm, according to Sramik (257). This involves preheat ing the water to 80 C, adding lime, filtering, saturating with CO, but not below pH 9, and refiltering. The recovered CaCO is chemically pure. The nature of the deposits on turbine blades and effect on efficiency have been discussed by Kot and Lobanov (258). 

The recovery process of reaction heat is composed of converter, boiler or heater for feed water of boilers and interchangers (Preheater before converter) (Fig. 9.24). 

For the thermal destruction, the reactor temperature should be kept over 1000 °C that is possible under adiabatic conditions. On the other hand, lower temperatures are sufficient for catalytic decomposition of N2O at 500°C. Hence, the heat produced from N2O decomposition can be as well recovered as steam for preheaters and boilers [3]. 

On the other hand, 30 percent condensate recovery as a percentage of the steam generation rate is rather bad and represents sloppy operations and bad condensate recovery design practices. Very approximately, 10 percent of the cost of steam generation could be saved by recovering the condensate. The condensate contains few silicates, thus no blowdown (explained below) is needed, no chemical treatment or deaeration is required, and no energy that would otherwise be used to preheat the boiler feedwater will be wasted. 

My utility plant operators have observed that when they preheat their boiler combustion air from 20°C to 220°C, steam production drops by around 3 or 4 percent. They are forced to reduce the firing rate, because the radiant section of the boiler starts to overheat. With the radiant section just as hot with or without the air preheat, I would think that steam production would remain constant, so why would it drop off "... 

Adjusting the thermal efficiency of the components by raising or lowering the temperature by reduction of thermal efficiency of preheaters and boilers, by making heat exchangers co-current instead of counter-current, by reduction of peak metal temperature, etc. 

Oil can be fired more cheaply than coal (about 16.5 cents per ton during 1951). Sulfur in fuels (oil, coal, or gas) requires higher cold-end tempera tures in the air preheaters or economizers of boilers in order to prevent corrosion and fouling of the tubes. A 6 per cent sulfur fuel requires a temperature about 60 F higher than a 2 per cent fuel. 

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