Steam-Water Operations

Corrosive water must be avoided. If the column is made of stainless steel, the water should be low in chlorides (131). The author is familiar with one plant where steam-water operations were discontinued in stainless steel columns after it was found that chlorides in the water caused metal deterioration. Ideally, the water should contain a corrosion inhibitor. The corrosion inhibitor should be carefully selected, because several commercial inhibitors promote foaming in subsequent operation. 

Figur 11.6 Tray damage caused by a large step increase in cold water rate during a steam-water operation.

To prevent reboiler fouling, and accumulation of solids in the column during steam-water operations, an adequate water blowdown must be purged out of the column base. 

The column and its piping should be steamed to warm it up prior to the commencement of a steam-water operation (see Sec. 11.8). 

Guidelines 1 to 4 in Sec. 11.6 also apply to steam-water operation. 

Precautions reconunended for steaming the column are identical to guidelines 1 to 6 in Sec. 11.7. These problems are far less troublesome with steaming than with steam-water operations, because the only sources of cold in the column are atmospheric cooling and the initial temperature of the internals. 

A prestartup wash, leak-test, or steam-water operation. 

The cracked products leave as overhead materials, and coke deposits form on the inner surface of the dmm. To provide continuous operation, two dmms are used while one dmm is on-stream, the one off-stream is being cleaned, steamed, water-cooled, and decoked in the same time interval. The temperature in the coke dmm is in the range of 415—450°C with pressures in the range of 103—621 kPa (15—90 psi). Overhead products go to the fractionator, where naphtha and heating oil fractions are recovered. The nonvolatile material is combined with preheated fresh feed and returned to the furnace. The coke dmm is usually on stream for about 24 hours before becoming filled with porous coke, after which the coke is removed hydraulically. 

Fossil Fuel-Fired Plants. In modem, fossil fuel-fired power plants, the Rankine cycle typically operates as a closed loop. In describing the steam—water cycle of a modem Rankine cycle plant, it is easiest to start with the condensate system (see Fig. 1). Condensate is the water that remains after the steam employed by the plant s steam turbines exhausts into the plant s condenser, where it is collected for reuse in the cycle. Many modem power plants employ a series of heat exchangers to boost efficiency. As a first step, the condensate is heated in a series of heat exchangers, usually sheU-and-tube heat exchangers, by steam extracted from strategic locations on the plant s steam turbines (see HeaT-EXCHANGETECHNOLOGy). 

In addition to the fixed capital investment needed to purchase and install process equipment and auxiliaries, there is a continuous expenditure referred to as operating cost, which is needed to operate the process. The operating cost (or manufacturing cost or production cost) includes raw materials, mass-separating agents, utilities (fuel, electricity, steam, water, refrigerants, air, etc.), catalysts, additives, labor, and maintenance. The total annualized cost of a process is defined as follows ... 

The mining facility consists of four major operations 1) mining, ore extraction and transportation, 2) ore processing - treatment with chemical solvents to remove minerals, 3) removing impurities and 4) utilities e.g., electricity, steam, water, air and natural gas provided by the facility s power plant and by off-site suppliers. Accidents in any of these operations can stop the whole process. 

Are equipment, steam, water, air and electronic outlets arranged to keep aisles and operating floor areas clear of hoses and cables ... 

Second, any valve which has been designed to operate on steam should not be expected to work at its best when supplied with a mixture of steam, water and dirt. A separator, drained through a steam trap, will remove virtually all the water from the steam entering the pressure-reducing set. The baffle type separators are found to be effective over a wide range of flow rates. 

Ejectors, steam/water requirements, 371 Electrical charge on tanks, 537 Electrical precipaiaiors, 280 Applications, 280, 282 Concept of operation, 281 Emergency relief, 450 Engineering, plant development, 46 Equipment symbols, 19—2 L Abbreviations, 25 Instruments, 21, 26. 29 Piping, 22 Valve codes, 26 Equivalent feel (flow), 86 Estimated design calculation time,... 

NOTE Almost all types of commercial or industrial boilers, of whatever type, size, and application, must be provided with fully softened FW as an absolute minimum form of external water treatment. This requirement includes electrical resistance boilers. Probable exceptions to this rule are HW heating boilers and steam boilers operating at below 15 psig and receiving in excess of 95% returned condensate. 

Typically, industrial WT boilers operate at pressures within the 100 to 650 psig range (sometimes up to 900-950 psig) and are rated for steam capacities within the range 40,000 to 200,000 lb/hr (5-21 kg/s) and steam temperatures of up to, say, 900 °F (482 °C). Industrial boiler designs tend to rely on natural, internal steam-water circulation. 

Boiler operational management processes provide for various daily procedures, maintenance routines and checks, including attending to BD, ash removal (where solid fuels are used), and the monitoring and control of fuel and MU water consumption, steam production, operating pressures, air and flue-gas temperatures, and FW and CR flows. 

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