Flue-gas side

Cleaning procedures include an internal washdown with a 0.5 to 2% soda ash solution, using a high-pressure jet. All wash water must be drained and deposits removed from the boiler. Usually, all external surfaces of the boiler are cleaned as well, in addition to the flue gas side of the economizer, air heater, and ID fans. 

Conventional Economizers Conventional economizers can be constructed from relatively inejq)ensive materials, such as low-alloy carbon steels, if they will be operated dry on the gas side, with flue gas side metal temperatures above the acid dew point. This practice is done to protect the economizer from corrosion, caused by the acidic flue gas condensate. Conventional economizers can also be con-... 

These objectives are equally important in the operation of fired boilers whose principles of operation on the fire-side and flue-gas side are essentially the same as those of process-plant-fired heaters. 

Procedures for finding the pressure drop on the flue gas side, the draft requirements and other aspects of stack design are presented briefly by Wimpress. 

Table 9 presents typical results from an operation extending beyond 7200 sec in duration and compares them to the yield from the predictive model simulation. The conditions under which these results were obtained were flow rates of 0.57 g/sec (both for naphtha and for steam) and 17.8 g/sec (flue gas) at inlet temperatures of 723 K on the process side and 1298 K on the flue gas side. This design shows considerable promise for controlling product composition and conversion with short residence time. 

The same heat output is achieved with a heat exchance area of 85 m as with 29 m though the air-side pressure drop increases from 100 to 6500 Pa and the flue gas-side pressure drop from 100 to 1600 Pa. The greater increase of air-side pressure drop derives from the fact that in addition of changing the number of pipes also the distance between pipes was changed. 

On the flue gas side there could be problems of particulate deposition (see Section 16.3) and possibly corrosion that coupled with the deposits on the hot oil side, may lead to operating difficulties. The quality of the fuel and the maintenance of good combustion conditions will be factors in the fouling process. 

On the flue gas side, however, this rule does not apply. Although an increase in waste gas velocity increases the convective heat transfer, it requires that the gas passages be reduced in cross-sectional area (for a given quantity of gases), and thereby decreases gas radiation from the CO2 and H2O vapor in the poc. The net result may actually decrease the total heat transfer on the gas side of a recuperator. 

Recuperators are usually designed with very low pressure drop on the flue gas side. In a shell-and-tube recuperator, the flue gas is generally on the shell side, with the air in the tubes, requiring more AP. In a vertical pipe-in-pipe recuperator such as a stack or radiation recuperator, the flue gas goes up the middle pipe (a) to take advantage of the additional stack or natural convection draft, (b) to allow a wider gas... 

Reducing air in-leakage in the convective section may correct this problem. Perhaps the convective tube bank is partially plugged on the flue-gas side. A pressure survey with a draft gauge is the first step in identifying the restriction that limits draft. Occasionally, the size of the secondary air registers can be increased. 

Furnace-draft gauge readings can pinpoint restrictions to flow on the flue-gas side of the convective section. Excessive draft at the inlet to the convective section causes cold air to be sucked in and wastes energy (see Chapter 15). 

The measured fuel flows, arch oxygen composition, and high pressure steam drum heat balance confirm that the heat duties calculated from the process side (as opposed to the flue gas side) are most accurate, as would be expected. The high pressure steam system and boiler feed water measurements impact significantly on the convection section heat balance since boiler feed water preheat and steam superheat duties make up the majority of the convection section duty. The high pressure steam import flow, and the expected versus measured and calculated S5mthesis gas compressor steam turbine performance further support that the process side, and not the flue gas side measurements are the most accurate. 

The first two equations symbolize heat balances for th zones at the flue gas side. The balances for the coil... 

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