Boiler, waste-heat

Process Steam Generation. Steam generated in the process sections of the plant may be at the highest plant pressure level or an intermediate level. Also, the process area may have fired boilers, waste heat boilers, or both. There may be crossties between utility and process generated steam levels. Enough controls must be provided to balance far-ranging steam systems and protect the most critical units in the event of boiler feedwater shortage situations. 

Waste-heat boilers. Waste-heat boilers can be designed to accept any grade of waste heat to produce steam or hot water. Designs can be based on water-tube boilers, shell and tube boilers, or a combination of the two. 

Cast iron sectional boilers Steel boilers Electrode boilers Steam generators Vertical shell boilers Horizontal shell boilers Watertube boilers Waste heat boilers Fluid bed boilers... 

Heat release coefficients Heat-recovery boiler, see Boiler, waste heat 13... 

Gas data gas source waste heat boiler waste heat boiler... 

Boilers should be thoroughly inspected by a competent person before being taken into use for the first time and subsequently once every 14 months. In the case of certain water-tube boilers, waste-heat boilers and heat exchangers that are of fusion welded or solid forged construction the period of inspection is 26 months. 

Waste activated sludge Waste biomass Waste-derived fuels Waste disposal Waste-heat boiler... 

Incineration. Gases sufftciendy concentrated to support combustion are burned in waste-heat boilers, dares, or used for fuel. Typical pollutants treated by incineration are hydrocarbons, other organic solvents and blowdown gases, H2S, HCN, CO, H2, NH, and mercaptans. VOC... 

Some beehive ovens, having various improvements and additions of waste heat boilers, thereby allowing heat recovery from the combustion products, may stiU be in operation. Generally, however, the beehive oven has been replaced by waH-heated, horizontal chamber, ie, slot, ovens in which higher temperatures can be achieved as well as a better control over the quality of the coke. Modem slot-type coke ovens are approximately 15 m long, approximately 6 m high, and the width is chosen to suit the carbonization behavior of the coal to be processed. For example, the most common widths are ca 0.5 m, but some ovens may be as narrow as 0.3 m, or as wide as 0.6 m. 

The gas, along with entrained ash and char particles, which are subjected to further gasification in the large space above the fluid bed, exit the gasifier at 954—1010°C. The hot gas is passed through a waste-heat boiler to recover the sensible heat, and then through a dry cyclone. SoHd particles are removed in both units. The gas is further cooled and cleaned by wet scmbbing, and if required, an electrostatic precipitator is included in the gas-treatment stream. 

The hot gases from the combustor, temperature controlled to 980°C by excess air, are expanded through the gas turbine, driving the air compressor and generating electricity. Sensible heat in the gas turbine exhaust is recovered in a waste heat boiler by generating steam for additional electrical power production. 

The latest installations incorporate a waste heat boiler in the off-gas cleaning system to recover sensible heat from the rotary kiln off-gas. There is sufficient sensible heat in the off-gas from the SL/RN process to generate 500 to 700 kWh/t of DRJ, depending on the type of reductant used. 

Reducing gas is generated from natural gas in a conventional steam reformer. The natural gas is preheated, desulfurized, mixed with steam, further heated, and reformed in catalyst-filled reformer tubes at 760°C. The reformed gas is cooled to 350°C in a waste heat boiler, passed through a shift converter to increase the content, mixed with clean recycled top gas, heated to 830°C in an indirect-fired heater, then injected into reactor 4. 

The combined flue dust from waste heat boiler and electrostatic precipitator, including dust from the ventilation system, is collected in a bin and recirculated to the mixing and pelletizing step, where it is used as a binding reagent. 

Fig. 1. Effect of energy use on total cost where total cost is the sum of capital and energy costs for the lifetime of the plant, discounted to present value. Point D corresponds to the design point if the designer uses an energy price that is low by a factor of four in projected energy price. Effects on costs of (a) pressure drop in piping, (b) pressure drop in exchangers, (c) heat loss through insulation, (d) reflux use, and (e) energy recovery through waste-heat boiler...

Waste-Heat Boiler. In a waste-heat boder (Fig. 6), the approach AT sets both the amount of the unrecovered energy and the amount of heat-exchange surface. When terms are added for energy value, and surface cost, the optimum occurs when... 

Fig. 6. AT in a waste-heat boiler (a) schematic (b) corresponding graphic representation.

Harvested and defivered whole, the trees are dried ia an air-supported fiber glass dome stmcture over a 30-d period by usiag waste heat from the combustioa process ia the adjaceat plant (Pig. 5). Trees leave the dome on the conveyor and, at the boiler wall, batches ate cut iato sectioas to fit the boiler. These sectioas are about 8.5 mloag for the 100-MW facility studied by EPRI and the Mianesota Power Light Company. 

The Claus process is the most widely used to convert hydrogen sulfide to sulfur. The process, developed by C. F. Claus in 1883, was significantly modified in the late 1930s by I. G. Farbenindustrie AG, but did not become widely used until the 1950s. Figure 5 illustrates the basic process scheme. A Claus sulfur recovery unit consists of a combustion furnace, waste heat boiler, sulfur condenser, and a series of catalytic stages each of which employs reheat, catalyst bed, and sulfur condenser. Typically, two or three catalytic stages are employed. 

A derivative of the Claus process is the Recycle Selectox process, developed by Parsons and Unocal and Hcensed through UOP. Once-Thm Selectox is suitable for very lean acid gas streams (1—5 mol % hydrogen sulfide), which cannot be effectively processed in a Claus unit. As shown in Figure 9, the process is similar to a standard Claus plant, except that the thermal combustor and waste heat boiler have been replaced with a catalytic reactor. The Selectox catalyst promotes the selective oxidation of hydrogen sulfide to sulfur dioxide, ie, hydrocarbons in the feed are not oxidized. These plants typically employ two Claus catalytic stages downstream of the Selectox reactor, to achieve an overall sulfur recovery of 90—95%. 

The sulfur dioxide of reaction 1 is cooled in a waste-heat boiler, freed from calcine, and converted to trioxide. The oxidation and conversion to sulfuric acid is conducted in a conventional acid plant (see also Sulfuric acid and sulfur trioxide). 

The coarse calciae cooler operates at 300°C, while the waste-heat boiler cools the gas to 350°C. The tubes ia the boilers have a chain-shaking arrangement operated by paeumatic hammers. Steam productioa is 0.78 kg/kg of dry coaceatrate. The only trouble with dust reported is ia the connection betweea the reactor and waste-heat boiler. It is necessary to cool the gas stream quickly to avoid sulfation, but even so the carry-over calciae coataias oa the order of four times more sulfate than the coarse overflow. In this plant, the composite calciae is 0.1% sulfide and 2.2% sulfate sulfur. 

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