Inerts blanketing, condenser

The presence of water, or water vapour, affects the chemistry of thermal modification and heat transfer within the wood (Burmester, 1981). Under dry treatment conditions, the wood is dried prior to thermal modification, or water is removed by the use of an open system, or a recirculating system equipped with a condenser. In closed systems, water evaporated from the wood remains as high-pressure steam during the process. Steam can also be injected into the reactor to act as a heat-transfer medium, and can additionally act as an inert blanket to limit oxidative processes. Such steam treatment processes are referred to as hygrothermal treatments. Where the wood is heated in water, this is known as a hydrothermal process. Hydrothermal treatments have been extensively studied as a... 

There are P I diagrams for individual utilities such as steam, steam condensate, cooling water, heat transfer media in general, compressed air, fuel, refrigerants, and inert blanketing gases, and how they are piped up to the process equipment. Connections for utility streams are shown on the mechanical flowsheet, and their conditions and flow quantities usually appear on the process flowsheet. 

Gas purging should be avoided when inert blanketing in the condenser is a concern or when the gas can be troublesome in downstream equipment. 

The vapor product system in Fig. 9.3 is one example of a system that favors location C (60, 369). If the relief valve is upstream of the condenser (location A), the air condenser will be inert-blanketed and become completely ineffective during a power failure. A relief valve on the reflux drum (location C) will meiximize condensation. Location C also offers easier access to maintenance and a shorter blowdown line. 

Condenser design determines the extent of Rayleigh fractionation. Vertical upflow condensers ("vent or "inerts condensers (e.g.. Fig. 15.14c,e see Sec. 15.11) are intended to operate as Rayleigh fractionators. Other condensers which exhibit this fractionation behavior are unbaffled vertical downflow shell-side condensers (if baffles are included, they would interrupt the free fall of liquid), emd multipass horizontal in-tube condensers where liquid is segregated at the end of each pass. One case was reported (381) where this behavior caused severe inerts blanketing in an unbafiled, downflow shell-side condenser. 

Figure 15.14a,6 shows preferred vent locations on the common types of in-shell horizontal condensers. Gilmour (134) described a case history of inert blanketing in the condenser shown in Fig. 15.15a before the vents were added a similar problem has been reported by others (381). Figure 15.156 shows a good vent location on a two-pass, in-tube condenser. 

An inert blanketing problem in a condenser shell can often be diagnosed by measuring surface temperature. Areas blanketed by inerts tend to be considerably cooler. If safety regulations permit, feeling the shell by hand at different spots can sometimes be an effective surface thermometer. 

Capacity of a horizontal, in-shell condenser was well below design. Inlet vapor entered in the middle ends were inert-blanketed. Vents solved problem. Ensure adequate venting. 

Vapor entering a vertical downflow in-sbell condenser contained a hig -molecular-weig t condensable material and a low-molecular-wei t inert Poor condensation was caused by channeling that caused inert blanketing. Use sealing strips ensure adequate condenser pressure drop. 

Vapor Treatment. The vapors from the tank space can be sent to a treatment system (condenser, absorption, etc.) before venting. The system shown in Fig. 9.1 uses a vacuum-pressure relief valve which allows air in from the atmosphere when the liquid level falls (Fig. 9.1a) but forces the vapor through a treatment system when the tank is filled (Fig. 9.16). If inert gas blanketing is required, because of the flammable nature of the material, then a similar system can be adopted which draws inert gas rather than air when the liquid level falls. 

Another example of pressure control by variable heat transfer coefficient is a vacuum condenser. The vacuum system pulls the inerts out through a vent. The control valve between the condenser and vacuum system varies the amount of inerts leaving the condenser. If the pressure gets too high, the control valve opens to pull out more inerts and produce a smaller tube area blanketed by inerts. Since relatively stagnant inerts have poorer heat transfer than condensing vapors, additional inerts... 

The ethane is much lighter than the methyl chloride, so it accumulates in the condenser and acts essentially like an inert substance that blankets the condenser. The effect of the inert substance can be considered to reduce either (1) the bubblepoint temperature, thus reducing the differential temperature driving force and reducing heat transfer, or (2) the effective heat transfer area. Either effect is a reduction in heat transfer. So if the ethane is not vented off during the batch, the pressure cannot be controlled even with the chilled water valve wide open. 

Composition and temperature profiles in the vapor phase at the top of the condenser tube are shown in Figure 15.8. Note how the concentration of inert gas increases towards the interface. The noncondensing nitrogen is acting as a blanket, making it harder for the methanol to condense. 

DEHUMIDIFYING CONDENSERS. A condenser for mixtures of vapors and noncondensable gases is shown in Fig. 15.9. It is set vertically, not horizontally like most condensers for vapor containing no noncondensable gas also, vapor is condensed inside the tubes, not outside, and the coolant flows through the shell. This provides a positive sweep of the vapor gas mixture through the tubes and avoids the formation of any stagnant pockets of inert gas that might blanket the heat-transfer surface. The modified lower head acts to separate the condensate from the uncondensed vapor and gas. 

When instrument connections are purged by an inert gas, adequate venting must be provided at the overhead condenser to prevent gas blanketing. In one incident (239), condensation was impaired after a nitrogen-purged instrument was added to the column. Gas-purged instrument connections should be avoided if the gas can be troublesome in the condenser or in downstream equipment. 

Refineiy Debutanizer The ability to condense the overiiead product was lost because of vapor blanketing in the condenser shell. Venting solved the problem. A newly installed, nitrogen-purged instrument caused the problem. Ensure adequate venting when inerts are likely to be present... 

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