Combined heat power

Tjman, M. (2005). Case study of the benefits of combined heat power (CHP). linergy use in dairy processing. Bull. Int. Dairy Fed. 401, 23-31. 

The economics of power generation can be highly improved if the heat, which otherwise would be wasted, can be sold. Therefore the combined heat-power systems ( co-generation ) provide a solution with maximum economic benefits. The best way of waste heat utilization is the use of heat in a district heating system, which can take up the substantial heat load. 

Examine the efficiency of a combined heat power cycle that should supply the load required in the Example 10.3. Consider superheated steam at 60 bar and 540 C. The stream for heating is extracted at a 50% ratio. Assume ideal Rankine cycle with steam exit pressure at 3 bar. 

The high-temperature technology is able to create so-called r enerative cells which can work either in the electrolyzer mode or in the fuel cell (SOFC) mode (see section 7.2.2.). Hot Elly efficiency is expected to rise up to 111 % in the future including the utilization of the process heat in the combined heat power operation mode [53]. 

The German industry is pursuing the design of a natural gas fueled SOFC with a self-supporting structure of an electrolyte of 100 fim thickness and an area of 50 by 50 mm. Developmental steps of SOFC in the Siemens company have started with a 50 W unit in 1993, passed 370 W, 1.8 kW, 10.8 kW, and eventually reached 20 kW in 1996. The design specifications of a SOFC combined heat power plant (see Fig. 7-5) are an efficiency of > 50 %, a fuel utilization of > 90 %, a thermal cyclability of > 100 cycles, and an operational lifetime of > 40,000 hours. A 20 % pre-reforming of the natural gas fuel is required. Its construction is expected within the next 2-3 years [40]. 

Ceramic Fuel Cells Limited (CFC Ltd.) (2006a). Combined Heat Power (micro-CHP) Domestic Demonstration Unit. Ceramic Fuel Cells Limited. 

Continued installation of combined heat/power systems. The use of fuel... 

Poly-generation strategies (for combined heat, power and chemical production applications) are also considered, with particular reference to recent technological innovations in hot gas cleaning and conditioning these have been developed to achieve the required improvements in syngas quality and have been validated under industrially relevant conditions. 

Anon, (2002). Combined heat, power and chemicals the feasibility of gas turbine reactors. Report by David Reay and Associates in association with the partners. Agreement E/CA/00340/00/00/4576, ETSU. Final report June. 

Now that these tubs have served their purpose and have successfully delivered a luxury food to us, they will be placed in the bins here in the lobby of this lecture theatre, from where they will be carried by a cleaner to the wheeled rubbish containers on the street outside and picked up by a Veolia refuse truck contracted by Lewisham Council. The lorry will take them down the hill to the South East London Combined Heat Power waste station, where they will be incinerated to generate electricity. Azeri lithosphere will float off into London air, carrying its carbon load into the atmosphere. However, unlike the water cycle, there is no simple process to return released carbon to Caspian geology. 

A more complex utility is combined heat and power (or cogeneration). Here, the heat rejected hy a heat engine such as a steam turbine, gas turbine, or diesel engine is used as the hot utility. 

Now let us take a closer look at the two most commonly used heat engines (steam and gas turbines) to see whether they achieve this efficiency in practice. To make a quantitative assessment of any combined heat and power scheme, the grand composite curve should be used and the heat engine exhaust treated like any other utility. 

Example 6.5 The stream data for a heat recovery problem are given in Table 6.7. A problem table analysis for AT , = 20°C results in the heat cascade given in Table 6.8. The process also has a requirement for 7 MW of power. Two alternative combined heat and power schemes are to be compared economically. 

Figure 6.35 Alternative combined heat and power schemes for Example 6.4.

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. 

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. ... 

For most chemical plants, process steam is used at pressures of 1.825 MN/m" (250 psig), saturated or lower. When combined heat and power generation is economically justified, the steam may be generated at about 5.96 MN/m" (850 psig) appropriately superheated and used to drive back-pressure steam turbines passing out process steam at the required pressure level. 

The new marketplace of energy conversion will have many new and novel concepts in combined cycle power plants. Figure 1-1 shows the heat rates of these plants, present and future, and Figure 1-2 shows the efficiencies of the same plants. The plants referenced are the Simple Cycle Gas Turbine (SCGT) with firing temperatures of 2400 °F (1315 °C), Recuperative Gas Turbine (RGT), the Steam Turbine Plant (ST), the Combined Cycle Power Plant (CCPP), and the Advanced Combined Cycle Power Plants (ACCP) such as combined cycle power plants using Advanced Gas Turbine Cycles, and finally the ITybrid Power Plants (HPP). 

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