Steam supply, contamination

In large boiler plants, carryover is measured by employing a singleport sampling nozzle connected to a steam supply line between the top drum and the superheater. Sampling from superheaters is difficult, however, because a pump is needed to inject cool condensate water into a double-walled sample probe (via an attemperating nozzle). This is to remove the degrees of superheat and thus reduce the tendency for any contaminants to deposit in or on the sample probe, rather than be collected with the steam. 

With modern autoclaves, the major impediment of concern to successful sterilization is air in porous loads. Air may be present as a contaminant of the steam supply such that the temperatures theoretically achievable at particular steam pressures are depressed, or air may be present within the load, insulating it from the contact with the steam required for predictable lethality. 

Water and Drainage. Water is a potential source of microbiological contamination that cannot be excluded from aseptic manufacture. Its control becomes complicated by the variety of purposes for which it may be used and the various types of distribution system that may be encountered. Identifiable potential sources of contamination from water in aseptic manufacturing facilities include (a) ingredient water for sterile products, (b) water supplies for equipment and component cleaning, (c) water supplies to laundries, (d) water supplies for hand washing, and (e) steam supplies to autoclaves. 

These contaminants can enter the steam supply system with the makeup water or in process heat exchange equipment. They can exist in the boiler drum in relatively high concentrations without causing problems. It is only when they are carried over into the exiting steam that they enter the turbine. Efficient boiler drum separators can limit total dissolved solids to as little as 0.5 to 1.0 ppm. Silica is difficult to separate from the steam and must be controlled in the boiler feedwater. Care must also be taken with the fluid used to attemperate the steam exiting the superheater. Contaminated process returns can bypass the steam separation in the drum as attemperator fluid. This should be maintained at less than 1.0 ppm total dissolved solids. 

Contamination of the steam supply with CO, N, or light hydrocarbons... 

Improper demineralization will also leave carbonates in the BFW. These carbonates will break down in the boiler to produce CO. The COj contaminates the steam supply to reboilers, where it is trapped. The COj accumulates and dissolves in the steam condensate to produce corrosive carbonic acid, resulting in tube failure in the reboiler tube bundle. 

When steam in the cycle is lost or used in a process, the reduced volume of returning condensate is compensated for by introducing some level of MU water. The loss of water or steam from a steam system cycle may vary from 1 to 100%. The supply of MU (and to a lesser degree the addition of chemical treatments) provides a source of dissolved solid contaminants that can concentrate in the boiler until some predefined limit is reached. At this point, BD is required, the loss of which is also compensated for by the addition of further MU water. 

In most boiler plants, a high percentage of the generated steam is condensed after use and returned to the pre-boiler section, where it is supplemented with sufficient MU to meet the current total FW demand at any particular time. Because this returned condensate or condensate return (CR) generally comprises the greater part of the FW supplied to the boiler, any contamination of the condensate may result in contamination of the FW system that is ultimately transported into the boiler section itself. 

Additionally, comparison of MU water usage and steam production with chemical treatment supplied, fuel consumption records, and flue gas analysis will provides early warning signs of deposit formation. Water analysis records can indicate problems of process contamination, BW carryover, and inadequate oxygen scavenging (and therefore the potential for corrosion). 

Thermal desorption is a technology that physically separates volatile and some semivolatile contaminants from contaminated media. In thermal desorption, heated air is used to volatilize contaminants at temperatures below those used for incineration. There are both in situ and ex situ applications of the technology. Ex situ treatments typically are used to remediate soil, sediments, sludges, and filter cakes. In situ applications of the technology use injected steam, thermal blankets, or heat supplied by electrodes to volatilize contaminants, which are then removed using extraction wells. 

Heating of radioactive solutions, particularly under elevated pressure (e.g., steam sterilization), is also a matter of safety. In order to avoid any contaminated air to escape if a container or a seal is broken, autoclaves used for radioactive solutions should be placed inside negative-pressure sealed units. Autoclaves used for sterilizing high-energy y-emitting radiopharmaceuticals should in addition be supplied with proper lead shielding. 

Description Feeds are sent to USC cracking furnaces (1). Contaminants removal may be installed upstream. A portion of the cracking heat may be supplied by gas turbine exhaust. Pyrolysis occurs within the temperature-time requirements specific to the feedstock and product requirements. Rapid quenching preserves high-olefin yield and the waste heat generates high-pressure steam. Lower temperature waste heat is recovered in the downstream quench oil and quench water towers (2) and used in the recovery process. Pyrolysis fuel oil and gaso-... 

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