Venting considerations

In cases in which, often at start-up, hard-to-condense vapours which are also potentially toxic or environmentally unacceptable have to be vented, consideration should be given to scrubbing them. If a solvent recovery imit needs vacuum-making equipment, a liquid ring vacuum pump can often also be used as a vapour scrubber in addition to its main role. 

Models are useful for safety/venting considerations. It is very useful to be able to extrapolate to different operating conditions and anticipate worst-case scenarios or investigate the possible effects of process factors. In this case one maybe better prepared to tackle situations that might not always be apparent from the outset. 

Gating for reaction injection molding requires laminar flow and a built in after mixer as part of the gate design. Structural foam and RIM molds require nonconventional gating and venting considerations and the mold designer and the molder should be consulted. 

Sampling ndAnalysis Guidelines. As a general safety consideration, ah gases should be vented to an external area and whenever possible, inert gases should be used as the test gas for piping systems. 

Sterile Filtration of Gases. Primary appHcations for sterile gas filtration are the sterilization of fermentor inlet air, fermentor vent gas, vents on water for injection tanks, and vacuum break filters during lyophilization. Operational and process considerations apply. Typically, the membrane in gas... 

Dissolved Minerals. The most significant source of minerals for sustainable recovery may be ocean waters which contain nearly all the known elements in some degree of solution. Production of dissolved minerals from seawater is limited to fresh water, magnesium, magnesium compounds (qv), salt, bromine, and heavy water, ie, deuterium oxide. Considerable development of techniques for recovery of copper, gold, and uranium by solution or bacterial methods has been carried out in several countries for appHcation onshore. These methods are expected to be fully transferable to the marine environment (5). The potential for extraction of dissolved materials from naturally enriched sources, such as hydrothermal vents, may be high. 

Great care is needed in the design of autoclaves and sterilization cycles because of the requirement for the presence of moisture. The autoclave must be loaded to allow complete steam penetration to occur in all parts of the load before timing of the sterilization cycle commences. The time required for complete penetration, the so-called heat-up time, varies with different autoclave constmction and different types of loads and packaging materials. The time may not exceed specific limits in order to guarantee reproducibility and, for porous loads, saturated steam. The volume of each container has a considerable effect on the heatup time whenever fluids are sterilized. Thermocouples led into the chamber through a special connector are often employed to determine heatup times and peak temperatures. The pressure is refleved at the end of each sterilization cycle. Either vented containers must be used or... 

One important consideration in any catalyst oxidation process for a complex mixture in the exhaust stream is the possible formation of hazardous incomplete oxidation products. Whereas the concentration in the effluent may be reduced to acceptable levels by mild basic aqueous scmbbing or additional vent gas treatment, studying the kinetics of the mixture and optimizing the destmction cycle can drastically reduce the potential for such emissions. 

Safety Considerations Design and location of storage tanks, vents, piping, and connections are specified by state fire marshals, underwriters codes, and local ordinances. In NFPA 30, Flammable and Combustible Liquids Code, 1993 (published by the National Fire Protection Association, Quincy, Mass.), liquid petroleum fuels are classified as follows for safety in handhng ... 

Special environmental considerations (including emergency venting, spills, or releases)... 

Noise control is worth mentioning. The turboexpander and axial compressors are noise producers and consideration must be given to the need for providing noise abatement. Silencers on vents and noise insulation housings on machines should be considered and have been proven effective. 

Oxidation processes may rely on pH adjustment to enhance the chemical reaction. Figure 16 illustrates the typical configuration of a chemical oxidation process. The m or engineering considerations for chemical oxidation include reaction kinetics, mass transfer, by-products, temperature, oxidant concentration, pH and vent gas scrubbing. 

Consideration of All Releases into the System - All releases tied into the closed system must be considered. In addition to PR valve discharges, these may include fuel gas compressor and absorber knockout drum drainage, vapors vented from water disengaging drums, feed diversion streams, closed drainage from equipment, vapor blowdowns and liquid pulldowns. 

Because of extreme venting conditions assumed, effective stack heights and resultant plumes from both 3- and 5-minute discharge conditions attain heights beyond the micro-meteorological conditions assumed in accepted computation models. It is therefore highly probable there will be considerably further atmospheric dispersion and diffusion of the VCM than predicted in the results shown. That is, the ground level concentration can be expected to be considerably lower than the values shown in Table 6. 

Designs and systems should minimize potential harmful exposures in both normal and emergency operations. This consideration affects the location of normal and emergency drains and vents. 

The liquid drained from a vessel may flash a considerable quantity of natural gas when it flows into an atmospheric drain header. The gas will find a way out of the piping system and will seek the closest exit to atmosphere that it can find. Thus, a sump collecting vessel drains must be vented to a safe location. 

Consideration shonld be given to reaction forces that develop dnring venting. 

Flame arrester pressure drops mnst he taken into consideration when selecting and specifying them, especially when they are installed on vent systems of low pressure storage tanks, snch as API-type tanks. If the total system pressure drop exceeds the design pressure of the tank, the tank will he overpressnred and may he strnctnrally damaged. Refer to Section 6.1 for additional discnssion of this topic. 

---