Steam Systems and Cogeneration

Most processes operate in the context of an existing site in which a number of processes are linked to the same utility system. The utility systems of most sites have evolved over a period of many years without fundamental questions being addressed as to the design and operation of the utility system. The picture is complicated by individual production processes on a site belonging to different business areas, each assessing investment proposals independently from one another and each planning for the future in terms of their own business. Yet, the efficiency of the site infrastructure and the required investment is of strategic importance and must be considered across the site as a whole, even if this crosses the boundaries of different business areas. 

There are a number of reasons site steam and power systems need to be studied in process design  

A grassroot utility system may need to be designed. However, this is rare, and most situations would involve modification of an existing system. 

An old utility system might need a revamp to replace old equipment. 

Modifications to the configuration might be required to an existing utility system to reduce its operating costs. 

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Utility systems as sources of waste. The principal sources of utility waste are associated with hot utilities (including cogeneration systems) and cold utilities. Furnaces, steam boilers, gas turbines, and diesel engines all produce waste from products of combustion. The principal problem here is the emission of carbon dioxide, oxides of sulfur and nitrogen, and particulates (metal oxides, unbumt... 

Alternatively, short-rotation hybrid poplar and selected grasses can be multicropped on an energy plantation in the U.S. Northwest and harvested for conversion to Hquid transportation fuels and cogenerated power for on-site use in a centrally located conversion plant. The salable products are Hquid biofuels and surplus steam and electric power. This type of design may be especially useful for larger land-based systems. 

Conventional fossil fuel-fired power plants, nuclear power faciUties, cogeneration systems, and combined-cycle faciUties all have one key feature in common some type of steam generator is employed to produce steam. Except for simple-cycle cogeneration faciUties, the steam is used to drive one or... 

Cog enera.tion in a. Steam System. The value of energy in a process stream can always be estimated from the theoretical work potential, ie, the deterrnination of how much power can be obtained by miming an ideal cycle between the actual temperature and the rejection temperature. However, in a steam system a more tangible approach is possible, because steam at high pressure can be let down through a turbine for power. The shaft work developed by the turbine is sometimes referred to as by-product power, and the process is referred to as cogeneration. 

As a precursor to discussing the fundamental waterside problems, two schematic drawings of steam cycles are provided. These examples (Figures 4.1 and 4.2) display the water-steam path and the key items of equipment in a FT boiler plant steam system cycle and a WT cogeneration steam system cycle. 

Finally, on the facility level an economic comparison of three cogeneration steam systems for a wood pulping mill was carried out [20], finding that economic and environmental optimisation could not be achieved simultaneously. 

This section covers system issues such as HHV, LHV, and cogeneration efficiency calculations, heat rate calculations, and cogeneration steam duty calculations. 

Large industrial operations with on-site needs for electricity and heat in the form of process steam, direct heat, and/or space heat. Typical Systems All cogeneration systems involve the operation... 

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