Boilers, cost

Table 1. Cost conqtarisons for wood pellets and pyrolysis from raw material to district heating in a 3 MW boiler. Costs in USD/MWh. All costs not included.

HP steam CHP HP fuel + boiler Once the fuel cost and boiler costs are known, all that remains is... 

Steam production is shown in pounds per hour as well as metric tons per hour. The price is shown per unit of steam production in U.S. dollars. The curves are based on an operating pressure of 650 psig. Correction factors are shown in Table 1-3 for other steam pressures. Also included in Table 1-3 is a factor for the use of an air preheater and a two boiler cost factor. 

The package boiler cost is based on complete shop assembly and transport by water and road to the site. The field-erected boiler supply is based on shipping the boiler parts by water and road to the site and complete erection at the site. 

Boiler cost estimates include fittings, refractory, insulation and cladding for outdoor installation, internal piping, platforms and stairs, burner and flame safety equipment, economizer, force-draft fan plus drive and soot blowers. 

A complete set of superheaters for a 100 MW combined heat and power boiler costs in excess of lm. The durability of superheaters is thus an important factor in determining the long-term production costs. Unplanned outages due to leaking superheaters are also very expensive. As well as causing corrosion problems, the build-up of deposits reduces the heat uptake to the superheaters which leads to lower efficiency. Consequently, ways are being sought to reduce superheater corrosion. 

Steam costs vary with the price of fuel. If steam is only generated at low pressure and not used for power generation in steam turbines, then the cost can be estimated from local fuel costs assuming a boiler efficiency of around 75 percent (but can be significantly higher) and distribution losses of perhaps another 10 percent, giving an overall efficiency of around 65 percent. 

Exampie A.3.1 The pressures for three steam mains have been set to the conditions given in Table A.l. Medium- and low-pressure steam are generated by expanding high-pressure steam through a steam turbine with an isentropic efficiency of 80 percent. The cost of fuel is 4.00 GJ and the cost of electricity is 0.07 h. Boiler feedwater is available at 100°C with a heat capacity... 

The problem with this approach is that if the steam generated in the boilers is at a very high pressure and/or the ratio of power to fuel costs is high, then the value of low-pressure steam can be extremely low or even negative. This is not sensible and discourages efficient use of low-pressure steam, since it leads to low-pressure steam with a value considerably less than its fuel value. 

Selection of the high pressure steam conditions is an economic optimisation based on energy savings and equipment costs. Heat recovery iato the high pressure system is usually available from the process ia the secondary reformer and ammonia converter effluents, and the flue gas ia the reformer convection section. Recovery is ia the form of latent, superheat, or high pressure boiler feedwater sensible heat. Low level heat recovery is limited by the operating conditions of the deaerator. 

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... 

E. Goodrich have burned a 10% tire chip mixture with coal (11—13). Tire grinding size reduction problems and deflvery costs have stymied projects based on combined tire and coal fuel. Transportation of tire scrap can cost 0.05 /kg, exclusive of grinding costs, thus tire-fired boilers are limited to areas with sample scrap tire suppHes, eg, large cities or tire manufacturers. The cost of burning one metric ton of tires per hour in an incinerator was ca 0.20—0.40 per tire in 1974, which increased to 0.35—0.70 per tire in 1987 (14). 

Another furnace that does not require fuel preparation is the stoker boiler, which was used by New York State Electric Gas Corporation (NYSEG) in its TDE tests. At NYSEG, the stoker boiler, which has a 1649°C (3000°E) flame temperature (as does the cyclone boiler), has routinely blended low quaUty coal, and more recently, wood chips with its standard coal to reduce fuel costs and improve combustion efficiency. In the tire-chip tests, NYSEG burned approximately 1100 t of tire chips (smaller than 5x5 cm) mixed with coal and monitored the emissions. The company determined that the emissions were similar to those from burning coal alone. In a second test-bum of 1900 t of TDE, magnetic separation equipment removed metal from the resulting ash, so that it could be recycled as a winter traction agent for roadways. 

As of the mid-1990s, many older conventional steam plants have been converted to combined cycle. The old boiler is removed and replaced by a combustion turbine and heat recovery steam generator. Although the cycle efficiency is not as high as completely new plants, substantial capital cost is avoided by the modification and reuse of existing steam turbine and auxiHary equipment. In many combined cycle power plants, steam is injected into the combustors of the combustion turbine to lower peak flame temperatures and consequendy lower NO. ... 

Overall comparison between amine and carbonate at elevated pressures shows that the amine usually removes carbon dioxide to a lower concentration at a lower capital cost but requires more maintenance and heat. The impact of the higher heat requirement depends on the individual situation. In many appHcations, heat used for regeneration is from low temperature process gas, suitable only for boiler feed water heating or low pressure steam generation, and it may not be usefiil in the overall plant heat balance. 

Ash content is also important. Ash discharge at high temperature, as molten ash from a slagging boiler, involves substantial amounts of sensible heat. However, the higher cost of washed coal of lower (about 10%) ash content does not always merit its use. Ash disposal and extra freight costs for high... 

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