Reheat scheme

Another approach is to decouple the heat transfer and the reaction. This includes reheat schemes [403] [455] [548] in which the process gas is heated in a heater followed by reforming reaction in an adiabatic reactor as illustrated in Figure 1.15. However, many steps are required to reheat the gas because of the strong endothermicity of the reaction. 

The Claus process is the most widely used to convert hydrogen sulfide to sulfur. The process, developed by C. F. Claus in 1883, was significantly modified in the late 1930s by I. G. Farbenindustrie AG, but did not become widely used until the 1950s. Figure 5 illustrates the basic process scheme. A Claus sulfur recovery unit consists of a combustion furnace, waste heat boiler, sulfur condenser, and a series of catalytic stages each of which employs reheat, catalyst bed, and sulfur condenser. Typically, two or three catalytic stages are employed. 

The SO2 thus formed can then be used to make H2SO4, can be treated with limestone, or can be converted to elemental sulfur. The conversion to elemental sulfur can be achieved either by the Claus process or by treating SO2 with a reductant such as carbon (Trail/Resox process). An attractive way of recovering sulfur is by reacting the SO2 with iron sulfide itself to form iron oxide and elemental sulfur. Thus, if the SO2 formed by the oxidation of iron sulfide is recirculated, elemental sulfur can be produced in a single step. The problem with this scheme is that the elemental sulfur needs to be separated from the exit stream by cooling, and the SO2 needs to be reheated. Karr, et al. ( ) and Schrodt and Best (7) carried out experiments to test the feasibility of this scheme. The latter authors, using coal ash as the sorbent material, concluded that sulfur recovery by this method is both technically and economically unattractive. The same may not be true for the iron oxide-silica sorbent. More studies are necessary before a definite conclusion can be drawn. 

A simple tandem reverse-flow reactor scheme has been proposed for this purpose [11] (Fig. 7.5). By condensing the sulfur formed in the reactor outlet and reheating the residual anhydrous inert gas stream, one obtains a thermally efficient integration of the elutive adsorbent regeneration into the reactor operation. The arrangement depicted represents an adsorptive equivalent to the reverse-flow reactor with removal of a hot side-stream [6]. 

The formation of nickel and iron carbonyls can take place in the presence of gaseous carbon monoxide in contact with metallic nickel or iron or their sulphides. The thermodynamics favor this reaction at low temperatures so the formation takes place during gas cooling. The consequences of any metal carbonyl slip into the gas treatment units depend very much on the treatment scheme, since any subsequent reheating (e.g., for a CO Shift) will tend to decompose the carbonyls back to the metals or their sulfides. 

In contrast, consider the response of schemes 16.4a,6, or e to a similar change. The drop in accumulator level will reduce distillate flow, while reflux flow rate will remain unaltered. The same quantity of reflux will enter the column, but at a lower temperature. It will be reheated upon entry by vapor condensation, ind this will increase liquid flow down the column. This is not the desired response. Eventually, the appropriate response will be established, but not until the control tray temperature drops and the temperature controller takes corrective action. In scheme 16.46, a subcooling disturbance disturbs at least the top part of the column. With the Fig. 16.4a and e schemes, it will distimb the entire column. 

A catch-and-release strategy has been used for the synthesis of 2-substituted benzofurans in a two-step approach (Scheme 4.21). Initially, polymer-supported triphosphine (PS-PPhj) was treated with a substituted 2-(bromoalkyl)-phenol to generate the corresponding supported (2-hydroxybenzyl)-triphenylphosphonium bromide. To obtain acceptable conversion, an initial dose of 2-(bromoalkyl)-phenol was added to PS-PPh2 swollen in DMF. This mixture was heated to 85 °C and held for 15 min. Upon cooling, a second dose of the phenol was added and the reaction mixture reheated using the same program. In the second step of the reaction, treatment of the supported (2-hydroxybenzyl)-triphenylphosphonium bromide with an acyl chloride... 

Fig. 6.25. Five-zone reheat furnace temperature control for best productivity, lowest fuel use. This control scheme allows quick recovery from production delays. PV = process variable SP = setpoint T/s = temperature sensor.

Two partial isothermal sections at 1200 and 1800°C in the molybdenum comer reported by [1970Sav] are given in Figs. 14 and 15 in comparison with the calculated ones. The experimental results were obtained on alloys with up to 12 mass% Mo and up to 0.5 mass% C annealed at 1200 and 1800°C for 120 and 25 h, respectively, then reheated electrically at the same temperatures and quenched in liquid nitrogen at an average rate of 600 K s One can see that the phase relationships shown in Fig. 15 cannot be considered as a stable diagram, taking into account the accepted in the current assessment reaction scheme. The (Mo) + (3 + a ternary phase field can be realized only if the reaction of the Ti phase crystallization at 1629°C, Pi, is suppressed. 

Number of circuits type of Single-circuit scheme typical of BWR no reheating of steam ... 

Figure A1.5 Typical scheme of coal-fired thermal power plant (AuthorAJser BillC https // commons.wikimedia.org/wiki/File PowerStation2.svg website approached January 26, 2016) (1) Cooling tower (2) cooling-water pump (3) transmission line (3-phase) (4) step-up transformer (3-phase) (5) electrical generator (3-phase) (6) low-pressure (LP) steam turbine (7) condensate pump (8) surface condenser (9) intermediate-pressure steam turbine (10) steam control valve (11) high-pressure (HP) steam turbine (12) deaerator (13) feedwater heater (14) coal conveyor (15) coal hopper (16) coal pulverizer (17) boiler steam drum (18) bottom ash hopper (19) superheater (20) forced draught (draft) fan (21) reheater (22) combustion air intake (23) economizer (24) air preheater (25) precipitator (26) induced-draught fan and (27) flue gas stack.

Scheme of steam reheat with Sodium Steam Steam... 

The velocity and temperature fields are coupled by viscosity and shear-reheating terms in the governing equations, and so the fully coupled system must be solved iteratively. An approach that exploits operator integration factors to rednce the multiple operator equation to an associated series of single-operator sub-problems has been adopted for the time-splitting scheme. This time splitting is described in detail by Maday et al. [4]. 

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