Utility waste

The principal sources of utility waste are associated with hot utilities (including cogeneration) and cold utilities. Furnaces, steam boilers, gas turbines, and diesel engines all produce waste as gaseous c bustion products. These combustion products contain carbon... 

Energy efficiency of the process. If the process requires a furnace or steam boiler to provide a hot utility, then any excessive use of the hot utility will produce excessive utility waste through excessive generation of CO2, NO, SO, particulates, etc. Improved heat recovery will reduce the overall demand for utilities and hence reduce utility waste. 

This is particularly important when considering the effect that combined heat and power generation (cogeneration) has on utility waste. 

Combined heat and power cogeneration). Combined heat and power generation can have a very significant effect on the generation of utility waste. However, great care must be taken to assess the effects on the correct basis. 

Fuel switch. The choice of fuel used in furnaces and steam boilers has a major effect on the gaseous utility waste from products of combustion. For example, a switch from coal to natural gas in a steam boiler can lead to a reduction in carbon dioxide emissions of typically 40 percent for the same heat released. This results from the lower carbon content of natural gas. In addition, it is likely that a switch from coal to natural gas also will lead to a considerable reduction in both SO, and NO, emissions, as we shall discuss later. 

Waste from steam systems. If steam is used as a hot utility, then inefficiencies in the steam system itself cause utility waste. Figure 10.9 shows a schematic representation of a steam system. Raw water from a river or other source is fed to the steam system. This is... 

The utility system also creates waste through products of combustion from boilers and furnaces and wastewater from water treatment, boiler blowdown, etc. Utility waste minimization is in general terms a question of ... 

In Chap. 10, modification of the process for reducing process waste was considered in detail. It also was concluded that to minimize utility waste, the single most effective measure would be improved heat recovery. The energy-targeting methods presented in Chaps. 6 and 7 maximize heat recovery for a given set of process conditions. However, the process conditions can be changed to improve the heat recovery further. 

The need to meet environmental regulations can affect processing costs. Undesirable air emissions may have to be eliminated and Hquid effluents and soHd residues treated and disposed of by incineration or/and landfilling. It is possible for biomass conversion processes that utilize waste feedstocks to combine waste disposal and treatment with energy and/or biofuel production so that credits can be taken for negative feedstock costs and tipping or receiving fees. 

Refractories made usiag alumiaas are used ia the iroa and steel, chemical and petroleum, ceramics and glass manufacture, minerals processiag (cement, lime, etc), pubHc utilities, waste iaciaeration, and power generation iadustries. 

Although rice bran is still a wasted product all over the world, recent scientific studies have recognized its potential health benefits. This is a unique, nutrient-dense natural product which offers health benefits for a series of ailments. It is a food pharmacy worth considering not only for general health maintenance but also as a dietary supplement for serious health conditions. With the advent of unique stabilization technology rice bran, an under-utilized waste product, has now been made available as a highly nutritious, health-promoting food for humans. 

Production costs include capital-dependent costs, e.g. depreciation, interest, insurance, and taxes and operating costs such as costs of raw materials and auxiliaries, costs of utilities, waste-disposal costs, labour costs, maintenance costs, and overheads. 

The outer layers of the onion (the utility system) produce utility waste. The utility waste is products of fuel combustion, waste from the production of boiler feedwater for steam generation, and so on. However, the design of the utility system is closely tied together with the design of the heat exchanger network. Hence, in practice, the three outer layers should be considered as being the source of utility waste. 

The waste streams created by utility systems tend, on the whole, to be less environmentally harmful than process waste. Unfortunately, complacency would be misplaced. Even though utility waste tends to be less harmful than process waste, the quantities of utility waste tend to be larger than process waste. This sheer volume can then result in greater environmental impact than process waste. Gaseous combustion products contribute in various ways to the greenhouse effect, acid rain and can produce a direct health hazard because of the formation of smog. The aqueous waste generated by utility systems can also be a major problem if it is contaminated. 

Smith R and Petela EA (1992) Waste Minimization in the Process Industries Part 5 Utility Waste, Chem Eng, 523 16. 

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