Double-wall containment

To ensure timely action in the construction of an emergency dike, an attempt should be made to identify these possible situations and preplan for their occurrence. This preplanning should include a source of suitable machinery and diking materials. 

For chemicals that pose severe release hazards, one effective but costly way to provide spill containment is to use a double wall on the vessel or piping (CCPS, 1988b). Often construction materials for the outer (secondary) wall are the same as those of the primary inner wall. In case of inner-wall failure, 

Without a method or mechanism to detect a catastrophic, or even a small release from an inner wall, the use of a secondary outer wall is superfluous. A failure in the inner wall will certainly lead to a failure of the outer wall if the failure goes unnoticed and no action is taken. The secondary wall may delay the release, but release would be inevitable without annular space detection. Typical detection mechanisms include gas analyzers or pressure detectors for vapors, conductivity switches for liquids, or weep holes routed to drain systems that are periodically monitored (Prugh, 1992). A purge gas is sometimes used as a detection medium, to reveal a change in contaminants in the purge gas exhaust (CCPS, 1988b). 

If a leak does occur in the inner wall, a mechanism must exist to vent or drain the substance between the walls to a safe location. Connections must be provided to neutralize, clean, and hydrotest the annular space after a failure. The annular space must also receive preventive maintenance to assure its proper operation. Periodic checks of the integrity and reliability of leak detection systems should be required. 

The design of double-walled tanks requires some special considerations. For instance, some large cryogenic ammonia tanks are enclosed in secondary containers with leak-detection devices placed in the annular space (CCPS, 1988a). The Chemical Industry Association (of the United Kingdom) recommends a variation in double-containment design where only refrigerated vapors are present in the annular space between the two walls (Chemical Industry Association, 1975). 

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Scraped-Surface Crystallizer For relatively small-scale apph-cations a number of ciystallizer designs employing direct neat exchange between the shiny and a jacket or double wall containing a cooling medium have been developed. The heat-transfer surface is scraped or agitated in such a way that the deposits cannot build up. 

SafeChem, a subsidiary of Dow, has developed a handling system for chlorinated solvents that allows them to be used in closed-loop degreasing systems. The Safe-Tainer system uses two dedicated double wall containers one to hold fresh solvent and the other used solvent. The containers are connected to the cleaning equipment with zero dead volume, leak-free connections that prevent spills, leaks or vapour emissions during use. Used solvent is collected for recycling and professional disposal of any residues. The system minimises solvent use and release to the environment. A study carried out by Dow during a trial in... 

K is called the thermal conductivity, which for air at STP is. 023 W/(m K). One way to reduce this energy flow is to decrease the pressure. Cryogenic liquids (such as liquid nitrogen, which boils at 77K) are commonly stored in Dewar flasks, which are double-walled containers with an evacuated region between the walls. 

Figure 5.2 is an illustration of a vessel double-wall containment system. The annular space is kept at a higher pressure than the tank. Should a leak develop, the pressure in the annular space will fall because the flow capacity of the nitrogen pressure control system has been limited. A low pressure will occur, tripping a pressure alarm low (PAL), and alerting the operator to the leak. 

As with double-wall containment, enclosures are most effective when used with a leak-detection system. These systems should be continuously monitored and connected to both local and control room alarms as the system dictates (CCPS, 1988a). The monitoring and alarm instrumentation should be tested periodically to ensure that it will function as designed. This is discussed further in Chapter 6. 

As with double-wall containment systems, a transfer vessel s construction materials, design pressure, and temperature rating should at least equal those of the equipment being protected. Construction materials can differ if the transfer vessel will only be exposed to the corrosive process for an acceptably short duration. 

The most common method for storing hydrogen is to apply high pressure, which reduces the space necessary for storage. Hydrogen can also be liquefied and stored in special dewar double-walled containers at a temperature of -253°C. 

A concept of an evolutionary reactor is pursued with the joint French / German European Pressurized Water Reactor , EPR, a 1525 MW(e) plant with evolutionary steam generating system and innovative double-walled containment [20]. A three years basic design phase as a prerequisite for the beginning of the licensing procedure was finished in 1997. The characteristic feature is a core catcher to restrict a possible core melt to the power plant itself. The joint effort by Germany ind France, however, finds in both countries a situation where no further base load is required. The EPR, confirmed as a future standard in France, is projected to substitute decommissioned nuclear plants. 

Dewar flask /dew-er/ (vacuum flask) A double-walled container of thin glass with the space between the walls evacuated and sealed to stop conduction and convection of energy through it. The glass is often silvered to reduce radiation. 

Larger capacity storage vessels are basically the same double-walled containers, but the evacuated space is generally filled with powdered or layered insulated material. For economic reasons, the containers are usually cylindrical with dished ends, approximating the shape of a sphere, which would be expensive to build. Containers must be constructed to withstand the weights and pressures that will be encountered and adequately vented to permit the escape of evaporated gas. Containers also should be equipped with rupture discs on both inner and outer vessels to release pressure if the safety relief valves should fail. 

Dewan A double-walled container for cryogenic liquids, witti evacuated annulus and heat-reflective surfaces facing the vacuum. 

Cryogenic tanks (h) are built up to a volume of 100 m. Their insulation loss amounts to about 1% of the design liquid inventory per day. These low heat losses at storage temperatures of about 4 K are possible due to superinsulation, thermal radiation shields and deep vacuum in the clearances of the double-walled container. The heat radiation shields transport the heat to the pipes in which either nitrogen or helium itself evaporates. A typical layout is shown in Fig. 4.4 [4.2]. 

For the exterior wall of double-walled containers and for containments, reduction factors R2B for non-swelling exposure media may be reduced to R2. For exposure media that cause swelling in contact with PE or PP materials, the R2B reduction factors fisted in Table A. 11 are applicable for the exterior walls of double-walled containers and for containments [7]. 

Table A. 10 6 for outer wall of double-walled containers from PE and PP for exposure times of max. 6 months (top), and for containments from PE and PP and exposure times of max. 3 months (bottom) [7]...

The experimental setup is shown in Figure 6.45. The utilized glass (Borofloat) microreactor was fabricated by LTF (www.ltf-gmbh.com) and consists of a half round meandering channel (1 mm width). The illuminated volume is assumed to be equal to the channel volume of 0.27 ml. For the experiments, a solution of P-citronellol (0.1 M) and Ru( bpy)3Cl2 (0.001 M) in ethanol was filled in a cooled double-walled container, saturated with compressed air, and fed continuously to the microreactor in a loop over a time interval of 60-70 h. Samples were taken twice a... 

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