Energy, recovery

Energy recovery based on electricity input. The energy input, Wi (kWh), to be added into the system is determined by integrating the product of the voltage added at each measured current over the duration of the experiment, as 

The loss of power by the external resistor should be minimized by choosing a low-ohm resistor, resulting in loss of energy of only a few percent of the input energy. 

The energy input for the process can be converted to the equivalent number of moles of hydrogen on an energy basis, n, , using the energy content of hydrogen calculated from its heat of combustion, AHh2 (kJ/mol), as 

The efficiency of the process relative to only the electricity input, r]iy, is calculated as the ratio of the hydrogen produced to the energy content of the hydrogen recovered, or 

The value of l/rjw is the fraction of the produced hydrogen that was due to the energy in the electricity. Note that we could also express this efficiency based on the energy required and the energy content of the hydrogen produced as 

Process streams at high pressure or temperature, and those containing combustible material, contain energy that can be usefully recovered. Whether it is economic to recover the energy content of a particular stream depends on the value of the energy that can be 

Some processes, such as air separation, depend on efficient energy recovery for economic operation, and in all processes the efficient use of energy recovery techniques will reduce product cost. 

Kenney (1984) reviews the application of thermodynamic principles to energy recovery in the process industries. 

The amount of energy that can be recovered depends on the temperature, flow, heat capacity, and temperature change possible in each stream. A reasonable temperature driving force must be maintained to keep the exchanger area to a practical size. The most efficient exchanger will be the one in which the shell and tube flows are truly counter-current. Multiple tube pass exchangers are usually used for practical reasons. With multiple tube passes, the flow is part countercurrent and part cocurrent and temperature crosses can occur, which reduce the efficiency of heat recovery (see Chapter 12). 

The hot process streams leaving a reactor or a distillation column are frequently used to preheat the feed streams ( feed-effluent or feed-bottoms exchangers). 

In the pulp and paper industry there is a long tradition of waste incineration. For example, consider the combustion of bark and wood residues. Recent years have seen a growing interest in the use of other types of waste such as sludges and rejects for energy production purposes. The reasons are  

Due to their heating values and low content of harmftd substances, most types of waste from paper mills are suitable for energy recovery. Sludges and rejects are burned mainly in grate and fluidized bed combustion fadhties. Burning of sludges is also carried out in multiple hearth indneration plants. 

B Drying and ignition zone C Burning zone D After-burning zone 

Multiple hearth combustion plants, as shown schematically in Fig. 10.15, are especially suitable for the combustion of moist and paste-like waste. They have been used for decades in the paper industry for energy production from primary and biological sludges, often together with bark. The flue gas purification plant downstream from the multiple hearth furnaces usually consists of wet scrubbers to remove dust and sulfur compounds. The flue gas finally enters the stack via a mist eliminator. 

For sludge and reject incineration in paper mills the following conclusions concerning flue gas emissions are possible  

Traditionally, incineration has been used to reduce waste volume. It has also been used to produce inert residuals from hazardous waste. Emissions in the form of combustion gases and solid residuals from conventional incinerators have lead to much resistance to the widespread use of incineration. Nowadays, incineration technology is available which avoids the production of such emissions [25]. It would seem that the use of clean combustion technology to recover energy from waste otherwise destined to landfill has been accepted by European governments in and attempt to reduce landfill [57]. Two of the applications for plastics waste under investigation are the co-combustion of plastics waste with municipal solid waste as the main fuel and the use of 

Co-combustion of plastics waste with municipal solid waste 

Use of plastics waste as a fuel substitute in cement kilns 

Policies on incineration vary from country to country, for several reasons. First, the capacity to incinerate waste in an environmentally-acceptable manner varies, as does the capacity to deal with plastics waste by mechanical or chemical recycling. National heat demand and supply, fuel prices and taxation also plays a decisive role in the choice between landfill and incineration [66]. Energy recovery should not be seen as a solution to avoid recycling plastics, but rather as a last alternative to landfill should other routes to revaluation prove not to be viable. 

Various molding techniques can be employed to fabricate biofiber thermoset composites with relative ease even if continuous fiber reinforcements are preferred. 

McNaught, A.D. and Wilkinson, A. (1997) Compendium of Chemical Terminology, 2nd edn, Blackwell Scientific Publications, Oxford. 

Khosravi, E. and Musa, O.M. (2011) Thermally degradable thermosetting materials. Eur. Polym. J., 47, 465-473. 

Mathews, F.L. (1994) Techniques for manufacture of composites, in Handbook of Polymer Composites for Enpneers (ed. L. Hollaway), Woodhead Publishing, Cambridge. 

Brydson, J.A. (1999) Plastics Materials, 7th edn, Butterworth-Heinemann, Oxford. 

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There is a tradeoff between energy and capital cost i.e., there is an economic degree of energy recovery. Chapter 7 explains how this tradeoff can be carried out using energy and capital cost targets. 

In practice, the integer number of shells is evaluated from Eq. (7.18) for each side of the pinch. This maintains consistency between achieving maximum energy recovery and the corresponding minimum number of units target Nu- ixs- In summary, the number of shells target can be calculated from the basic stream data and an assumed value of Xp (or equivalently,... 

Example 16.1 The process stream data for a heat recovery network problem are given in Table 16.1. A problem table analysis on these data reveals that the minimum hot utility requirement for the process is 15 MW and the minimum cold utility requirement is 26 MW for a minimum allowable temperature diflFerence of 20°C. The analysis also reveals that the pinch is located at a temperature of 120°C for hot streams and 100°C for cold streams. Design a heat exchanger network for maximum energy recovery in the minimum number of units. 

The pinch design method developed earlier followed several rules and guidelines to allow design for minimum utility (or maximum energy recovery) in the minimum number of units. Occasionally, it appears not to be possible to create the appropriate matches because one or other of the design criteria cannot be satisfied. 

Figure 16.16 Maximum energy recovery design for Example 16.2.

Figure 16.23a shows the complete design, achieving maximum energy recovery in one more unit than the target minimum due to the inability to tick off streams below the pinch. 

Energy products Energy recovery Energy Security Act Energy storage Energy value Enflurane [13838-16-9]... 

The specific design most appropriate for biomass, waste combustion, and energy recovery depends on the kiads, amounts, and characteristics of the feed the ultimate energy form desired, eg, heat, steam, electric the relationship of the system to other units ia the plant, iadependent or iategrated whether recycling or co-combustion is practiced the disposal method for residues and environmental factors. 

Municipal Solid Waste. In the eady 1990s, the need to dispose of municipal soHd waste (MSW) ia U.S. cities has created a biofuels industry because there is Htde or no other recourse (107). Landfills and garbage dumps are being phased out ia many communities. Combustion of MSW, ie, mass-bum systems, and RDF, ie, refuse-derived fuel, has become an estabhshed waste disposal—energy recovery industry. 

Considerable laboratory work has also been done to develop pre- and post-digestion treatments that improve biodegradabiUty. A plateau of about 50—60% volatile soHds destmction efficiencies and energy recoveries in the product gas seems to exist for most methane fermentation systems. 

As of this writing, it has not been possible to use the seismic data which defines the volume of the reservoir to also determine the joint stmcture. Extended flow testing is the most direct measure of the efficiency and sustainabiUty of energy recovery from the reservoir. The use of chemical tracers in the circulating fluid can also provide valuable supporting data with regard to the multiplicity of flow paths and the transit time of fluid within the reservoir (37). 

An alternative starting network is one without stream spHts. The networks from the TI method maximize energy recovery and may introduce heat-load loops. Stream spHts ate not made in the initial steps of network invention. The ED method is proposed to be one in which heuristic rules and strategies would be used to improve the networks developed by the TI method. The importance of a thermodynamic base for evolutionary rules is stressed in this proposal, but there is no expHcit guidance for the evolutionary process. 

MER maximum energy recovery for given set of process streams... 

MER j, maximum energy recovery with network approach of AT... 

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...

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