Temperature process steam

Fig. 9.7. (Useful heai)/work as a function of process steam temperature (after Porter and Mastanaiah (21).

In the field of enhanced oil recovery, high steam pressures are required as could be provided by gas-cooled reactors water-cooled reactors would need an additional steam compression step [25]. Characteristic parameters are given in Table 2-2 for various designs. For the example of the Japanese industries, process steam temperature range and energy consumption structure are presented in Tables 2-3 and 2-4. 

Thermal stabihty of the foaming agent in the presence of high temperature steam is essential. Alkylaromatic sulfonates possess superior chemical stabihty at elevated temperatures (205,206). However, alpha-olefin sulfonates have sufficient chemical stabihty to justify their use at steam temperatures characteristic of most U.S. steamflood operations. Decomposition is a desulfonation process which is first order in both surfactant and acid concentrations (206). Because acid is generated in the decomposition, the process is autocatalytic. However, reservoir rock has a substantial buffering effect. 

SO2 gas is catalyticaHy oxidized to SO in a fixed bed reactor (converter) which operates adiabaticaHy in each catalyst pass. The heat of reaction raises the process gas temperature in the first pass to approximately 600°C (see Table 7). The temperature of hot gas exiting the first pass is then lowered to the desired second pass inlet temperature (430—450°C) by removing the heat of reaction in a steam superheater or second boiler. 

In the batchwise process the temperature can be raised to 80°C to promote levelness providing dyes not sensitive to reductive breakdown are used. In the continuous appHcation method the vat dye is padded onto fabric and dried under conditions that avoid migration, passed through a solution of sodium hydrosulfite and caustic, through a pad mangle, and then steamed in saturated steam for up to 60 s. 

Indirect. steam-tube dryer This is a bare metal cylinder provided with one or more rows of metal tubes installed longitudinally in the shell. It is suitable for operation up to available steam temperatures or in processes requiring water cooling of the tubes. 

The exhaust gases from a gas turbine contain substantial amounts of excess air, since the main combustion process has to be diluted to reduce the combustion temperature to well below that which could be obtained in stoichiometric combustion, because of the metallurgical limits on the gas turbine operating temperature. This excess air enables supplementary firing of the exhaust to take place and higher steam temperatures may then be obtained in the HRSG. 

Assume a 3-in. line. Design process temperature 320°F (Tp). Insulation 1 V2 -in- thick calcium silicate. Steam temperature 366°F (TJ. Ambient temperature 0°F (L,). 

The choice of boiler steam inlet conditions is usually dictated by the desire to achieve maximum output from the process steam flow. This requires high boiler steam pressure and temperature. However, there are practical considerations to observe. Above 40 bar more exacting feedwater treatment is necessary, and therefore it may be advantageous to maintain pressures below this figure. High steam and temperatures can also influence selection of boiler materials such as alloy steels. The upper limit for industrial applications is around 60 bara and 540°C. 

Superheated steam may be needed where steam distribution pipework in a plant is over extended distances, resulting in a loss of heat and increase in wetness of the steam. Another case may be where a process requires a temperature above the working pressure of the plant. The third case is where steam is used for turbines. Here it improves the performance of the turbine, where for every 6°C increase in steam temperature it can produce a saving of about 1 per cent reduction in steam consumption. Superheaters may also be supplied as independently fired units. These may be used when either the amount of superheated steam required is much less than the boiler evaporation or is only needed on an intermittent basis. 

Exiting steam from the roof and convection-pass cooling sections is collected in headers and typically passes through a primary superheater tube bundle, where a controlled amount of superheat is provided. In the superheater the steam discharges through an outlet header and across a spray attemperator (which provides the steam temperature control) and is then delivered to the control valves for distribution and subsequent use in a turbine or other items of process equipment. 

Turbines for electricity generation are limited in their efficiency, in part by moisture present in the steam but also by the partial condensation that occurs during the loss of energy when work is done by steam passing over the turbine blades. Thus, an increase in steam temperature over and above that required for saturation (through the use of a superheater) reduces the potential for condensation to occur and raises the efficiency of the combustion-to-electrical generation process, perhaps by 4 to 5%. 

The process of removing heat from superheated steam in order to control high pressure steam temperature and to tailor the steam for different, lower temperature and/or pressure applications. 

It can be seen that excess air and humidity in the combustion air both act to reduce the theoretical flame temperature. However, the excess air has the more significant effect. In some combustion processes, steam is injected into the combustion process to decrease the flame temperature to decrease NOx formation. This will be discussed later in Chapter 25. 

Commercial Masonite and Asplund boards and the asphalt-impregnated insulation board were sampled before any commercial heat treatment. The corresponding "thermomechanical" pulps had been produced by pressurized refining of steamed chips. The higher pre-steaming temperature used in the Masonite process resulted In a yield of about 85% as compared to a fiber yield of about 94% of the Asplund pulps, the remainder being dissolved. 

They generate relatively small amounts of nitrogen oxides other pollutants. Several companies have developed very low NOx units. Their high temperature exhaust may be used to make process steam and operate steam-driven chillers. A1-MW unit can cost 1,800/kW installed while a 5-MW unit may cost l,000/kW installed. 

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