Efficient heat recovery

In the process house water is generally heated from room temperature to 80-90 C and at the end of the process water is run away into the drain. This is absolutely uneconomic. Many of the modem machine is equipped with effective heat-exchangers, in which the outflowing hot water heats up the inflowing cold water and is only then discharged into the drain. 

Another possible source of recoverable heat is the waste heat contained in the condensate. Owing to the condensation problems, the flue gas temperature is around 200 C. If the flue gases are cooled down from 200 C to 50°C by boiler feed water or processing water, the result is considerable saving in energy. 

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The advantages of thermal incineration are that it is simple in concept, has a wide application, and results in almost complete destruction of pollutants with no liquid or solid residue. Thermal incineration provides an opportunity for heat recovery and has low maintenance requirements and low capital cost. Thermal incineration units for small or moderate exhaust streams are generally compact and light. Such units can be installed on a roof when the plant area is limited. = The main disadvantage is the auxiliary fuel cost, which is partly offset with an efficient heat-recovery system. The formation of nitric oxides during the combustion processes must be reduced by control of excess air temperature, fuel supply, and combustion air distribution at the burner inlet, The formation of thermal NO increases dramatically above 980 Table 13.10)... 

The major emissions from the combustion of fuel are C02, SO, NO and particulates14. The products of combustion are best minimized by making the process efficient in its use of energy through efficient heat recovery and avoiding unnecessary thermal oxidation of waste through minimization of process waste. Flue gas emissions can be minimized at source by ... 

The HI decomposition section flow sheets for both CEA and GA are heavily focused on efficient heat recovery. The basic principle for decomposition is the same for each. Reactive distillation of the HIX feed results in the production of hydrogen. The operating pressures in the distillation columns typically... 

As stated earlier in Section 1.2.1.1, equality of the heat capacity fluxes in the heat recovery sections is a crucial condition for efficient heat recovery. This condition is inherently fulfilled by the simultaneous and the counter-cocurrent concept. In the asymmetric concept the flow rates of the process streams must be adjusted accordingly. The requirement of equal heat capacity fluxes cannot be fulfilled in the symmetric concept due to the continuous side stream addition. However, besides these structural properties the design details are decisive for their specific performance and efficiency of individual solutions. 

For the example of methane steam reforming, Eq. (8) yields an acceleration factor of 4. Accordingly, the axial displacement of the reaction zone is a multiple of the axial displacement of thermal fronts. The difference of the axial displacement between the reaction front and the thermal front determines the axial profile of heat demand during the subsequent exothermic semicycle. Efficient heat recovery requires equal heat capacities of the process streams during both semicycles. The initial state can be restored by discrete heat sources distributed at equal distances along the catalytic part of the reactor. Each point source initiates a thermal wave that covers the distance to the next heating point (Fig. 1.13, right). This concept features... 

One way to improve carbon emissions and overall efficiency is to ensure that all furnace operations employ efficient heat recovery from the flue gas. Ideally the flue gas should be cooled in order to recover the heat of condensation of the water produced in the combustion process. 

The semicontinuous design allows a more efficient heat recovery than a batch system. Heat recovery is perfomed by means of indirect economizers (Figure 12). Steam produced in the bottom deodorized oil-cooling section is sent in a closed thermosiphon loop to the top bleached oil-heating section to heat the incoming oil. A single thermosiphon system has a recovery efficiency of 50%. With a double system, coupled with a low-pressure steam-production device, up to 75% of heat can be recovered. 

Higher operating temperature membranes enable more efficient heat recovery for stationary applications of PEMFCs. 

Consequently, the control of dioxin emissions from incinerators is one of the most urgent needs in environmental protection today [466, 516]. There are several treatment techniques presently in use, including the raising of the waste gas temperature to cause catalytic oxidative decomposition [516]. However, when the initial investment and mechanical complexity is taken into account, this method is not practicable for small-scale incinerators. A novel solution for this task would be to decompose dioxin and its derivatives at the dust filter using catal3dic oxidation, preferably below 473 K. This particular temperature is relevant since the waste gases are usually reduced to this temperature at the dust filter after efficient heat recovery. 

All heat requirements for the process are provided in the form of open steam at 400 psia. Some is used at the bottom of S-1 to strip HjS and the rest is fed to the twelfth plate in HT-1 to control the temperature of the hot towers and to compensate for heat losses and heat exchanger inefficiencies. Steam consumption is 1778/0.28 = 6400 mol/mol of DjO produced. This is much less than the 200,000 mol/mol DjO needed in water distillation. Additional energy in the amount of 680 kWh/kg D2O is used to circulate gas and pump liquid. This, however, is much less than is used in electrolysis or hydrogen distillation (Table 13.7). The low energy consumption of the GS process is due in large measure to the efficient heat recovery obtainable in the flow sheet Fig. 13.30, which follows Spevack s patent [S7]. 

The fundamental advantage of the use of fluidized catalysts for the highly exothermic hydrocarbon synthesis consists of a radical solution of the crucial heat transfer problem, which limited the yield per space and time in the case of fixed catalyst beds. The fluidized system presents the possibility of going to higher synthesis temperatures which means higher conversions with cheaper catalysts and more efficient heat recovery. This can be done without producing excessive amounts of carbon or methane. The yields of valuable olefinic hydrocarbons are very high in comparison with other hydrocarbon synthesis processes. 

The purge gas is burned as fuel in the primary reformer furnace, reducing the total fuel requirement for the reformer. Additional hydrogen must be produced to account for the purge gas loss and this increases the feed rate and the size of the reformer furnace. Nevertheless, the overall economics of the PSA unit, due in part to more efficient heat recovery, are superior to the conventional process with the low temperature shift and methanation reactors. Also, because the PSA unit removes all of the methane and carbon oxides from the hydrogen product, the operation of the reformer is independent of hydrogen product purity and, thus, can be operated at optimum conditions [4]. 

Kohayashi, H., Wu, KT, Bell, R.L., Thermochenrical Regenerator A High Efficiency Heat Recovery System for Oxy-Fired Glass Furnaces , DGG/AcerS Conference, Aachen, May 28, 2014. 

In nearly all ammonia plants the same material is used as both feedstock and fuel. The fuel requirements may be 40% of the total or mcwe, depending on the ext t to which heat recovery equipment is used. In previous years when fuel was inexpensive, many ammonia plante were built with minimum heat recovery facilities. Buividas et al. give an example of how the fuel requirement (natural gas) was decreased by 34% through more efficient energy use, which primarily included high-pressure steam generation and preheating combustion air to the reformers I7I, The decrease in total fuel plus feedstock reqiure-ment was about 15%. The increase in fuel efficiency was obtained at the expense of about 6% increase in plant investment costs. Table 6.8 shows the requirements for fuel plus feedstock that assume efficient heat recovery. 

The evaluation should include heat and material balances and should examine major consumers of the thermal energy outside the evaporator area. The most efficient heat-recovery system is usually one that can be used as a heat sink to receive waste heat, and the best location for this may be In another area which can readily receive a high-temperature stream for the evaporator. 

The flue gas at 1900°F must then be cooled to about 300°F to achieve efficient heat recovery. This heat is recovered in the convection section of the SMR. The process gas at 1600°F must then be cooled to about 100°F before final product purification. 

Calculate the amount of supplementary fuel that must be added to attain the desired combustion chamber temperature. In most cases the oxygen content of the feed gas will be high enough (over about 16%) to provide an adequate supply of oxygen for combustion of botli fuel and impurities, and the concentration of combustible impurities will be so low that their heat of combustion can be neglected. When precise calculations are required, or when the feed gas contains a solvent concentration over 2-3% of the LEL, it is necessary to take the heat of combustion of the gas impurities into account. The amount of fuel required can be estimated using a simple heat balance around the combustion chamber. The calculated amount of fuel should be increased as required to account for 5-10% heat losses from the incinerator. If the heat balance indicates that excess heat is available from combustion of the VOCs. a lower efficiency heat recovery unit can be used or. with a... 

Outotec, 2008. Sulfuric Acid Plants (Efficient Heat Recovery Improves Plant Economy). Outotec Oyj, Espoo, Finland. 

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