Steam reduction

Design methods for calciners In indirect heat calciners, heat transfer is primarily by radiation from the cylinder wall to the solids bed. The thermal efficiency ranges from 30 to 65 percent. By utilization of the furnace exhaust gases for preheated combustion air, steam reduction, or heat for other process steps, the thermal efficiency can e increased considerably. The limiting factors in heat transmission lie in the conductivity and radiation constants of the shell metal and solids bed. If the characteristics of these are known, equipment may be accurately sized by employing the Stefan-Boltzmann radiation equation. Apparent heat-transfer coefficients will range from 17 W/(m2 K) in low-temperature operations to 85 W/(m2 K) in high-temperature processes. 

Compressor K301 Motorization Following the HGU Steam Reduction When the compressor K301 driver is changed to motor, there could be a knock-on effect on steam balance as shut down of the turbine could reduce MP use by 625 t/day. The steam balance basis for assessing this option is Figure 20.4. 

Now let us look at what could happen if we take the route of sequence 2 of the implementation. This sequence starts with operational change, which is driver switch for boiler fan followed by steam reduction in the hydrogen plant, which is the same as the sequence 1 discussed previously. Thus, the focus is placed on the remaining options in the implementation sequence providing extra LP steam in HCU revamp, and F304 revamp for MP generation. 

After boiler driver switch and HGU steam reduction, the steam balance (Figure 20.4) features a small amount of LP dump at 48 t/day. Thus, to accommodate extra LP use in HCU at 150t/day, 102 t/day (150 — 48) LP has to be provided by additional boiler HP generation, which is cascaded through letdown valves, thus at... 

These rates uill be talgb for bleJt DOlecular uele t loads 1 and lou for blgh vapor pressure loads. Steam reduction vlth — baronetrlo interooadeneen ... 

Steam reduction involves heating to 550 to 660°F in the presence of large amounts of steam. In early refinery practice cylinder stock was exposed to steam in shellstills for many hours. Modem practice simply involves the use of steam in large amounts in a continuous distillation system. The effect of steam in reducing the boiling point is discussed in connection with Eq. (15-8) and Example 15-2. 

This is an endothermic reaction accompanied by an increase in the number of moles. High conversion is favored by high temperature and low pressure. The reduction in pressure is achieved in practice by the use of superheated steam as a diluent and by operating the reactor below atmospheric pressure. The steam in this case fulfills a dual purpose by also providing heat for the reaction. 

Figure 6.25a shows the same grand composite curve with two levels of saturated steam used as a hot utility. The steam system in Fig. 6.25a shows the low-pressure steam being desuperheated by injection of boiler feedwater after pressure reduction to maintain saturated conditions. Figure 6.256 shows again the same grand composite curve but with hot oil used as a hot utility. 

Fuel switch. The choice of fuel used in furnaces and steam boilers has a major effect on the gaseous utility waste from products of combustion. For example, a switch from coal to natural gas in a steam boiler can lead to a reduction in carbon dioxide emissions of typically 40 percent for the same heat released. This results from the lower carbon content of natural gas. In addition, it is likely that a switch from coal to natural gas also will lead to a considerable reduction in both SO, and NO, emissions, as we shall discuss later. 

Unsaturated hydrocarbons are present in nearly all products of the Clemmensen reduction of aromatic ketones and must be removed, if the hydrocarbon is requiral pure, by the above process. Secondary alcohols, often produced m small amount are not appreciably steam-volatile. 

Reduction of A-nitrosomethylaniline. Into a 1 litre round-bottomed flask, fitted with a reflux condenser, place 39 g. of A-nitroso-methylaniline and 75 g. of granulated tin. Add 150 ml. of concentrated hydrochloric acid in portions of 25 ml. (compare Section IV.34) do not add the second portion until the vigorous action produced by the previous portion has subsided, etc. Heat the reaction mixture on a water bath for 45 minutes, and allow to cool. Add cautiously a solution of 135 g. of sodium hydroxide in 175 ml. of water, and steam distil (see Fig. II, 40, 1) collect about 500 ml. of distillate. Saturate the solution with salt, separate the organic layer, extract the aqueous layer with 50 ml. of ether and combine the extract with the organic layer. Dry with anhydrous potassium carbonate, remove the ether on a water bath (compare Fig. II, 13, 4), and distil the residual liquid using an air bath (Fig. II, 5, 3). Collect the pure methylaniline at 193-194° as a colourless liquid. The yield is 23 g. 

The ester and catalj st are usually employed in equimoleciilar amounts. With R =CjHs (phenyl propionate), the products are o- and p-propiophenol with R = CH3 (phenyl acetate), o- and p-hydroxyacetophenone are formed. The nature of the product is influenced by the structure of the ester, by the temperature, the solvent and the amount of aluminium chloride used generally, low reaction temperatures favour the formation of p-hydroxy ketones. It is usually possible to separate the two hydroxy ketones by fractional distillation under diminished pressure through an efficient fractionating column or by steam distillation the ortho compounds, being chelated, are more volatile in steam It may be mentioned that Clemmensen reduction (compare Section IV,6) of the hj droxy ketones affords an excellent route to the substituted phenols. 

Thiophenols (or aryl mercaptans) are obtained by more vigorous reduction of sulphonyl chlorides (or of sulphinic acids), for example with zinc and dilute sulphuric acid, and are isolated by steam distillation ... 

It is possible to dispense with the extraction step if the oxidation section is operated at high propylene concentrations and low steam levels to give a concentrated absorber effluent. In this case, the solvent recovery column operates at total organic reflux to effect a2eotropic dehydration of the concentrated aqueous acryflc acid. This results in a reduction of aqueous waste at the cost of somewhat higher energy usage. 

SO2 absorbed with buffered citric acid solution. SO2 reduced with H2S to S. H2S produced on site by reduction of S with steam and methane. 

The burning of the ligneous portion of the black Hquor produces sufficient heat in the furnace to sustain flash drying of residual moisture, salt-cake reduction, and chemical smelting. The heat in the gas passing through the furnace, boiler, and economi2er produces steam for power and process. 

Assessments of control, operabiHty and part load performance of MHD—steam plants are discussed elsewhere (rl44 and rl45). Analyses have shown that relatively high plant efficiency can be maintained at part load, by reduction of fuel input, mass flow, and MHD combustor pressure. In order to achieve efficient part load operation the steam temperature to the turbine must be maintained. This is accompHshed by the use of flue gas recirculation in the heat recovery furnace at load conditions less than about 75% of fiiU load. 

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