Condensible blowdown drums

To Atmosphere Via Condensible Blowdown Drum - Releases which can be totally condensed may be routed to a condensible blowdown drum, which may be vented to the atmosphere. 

The header is normally a 80 mm diameter pipe (50 mm may be adequate for small units) and is routed via an overhead pipe rack (which is generally sloped) to a non-condensible blowdown drum. 

Select a condensible blowdown drum for condensible releases, rather than the non-condensible type. If a condensible blowdown drum is not suitable for handling the total blowdown service (e.g., if cold liquids are involved), then a combination of a condensible and a non-condensible drum may be used. 

The following are the principle advantages of condensible blowdown drums ... 

The disadvantages of condensible blowdown drums can be summarized as follows ... 

A typical non-condensible blowdown drum and its associated equipment and headers are illustrated in Figure 1. A single blowdown drum may be used for more than one process unit, if economically attractive. However, when this is done, all units served by it must be shut down in order to take the drum out of service, unless cross connections are made to another system of adequate capacity. Normally all closed safety valve discharges are combined into one header entering the drum, although separate headers and inlet nozzles are acceptable if economically advantageous. The following releases are also normally routed into the safety valve header ... 

Figure 1. Typical non-condensible blowdown drum arrangement.

Because of the continuous water flow through a condensible blowdown drum, it can safely handle cold or autorerrigerating releases only to the extent that effluent liquid and vapor temperatures remain above 0°C. 

A condensible blowdown tank, designed on a similar basis to that described above for phenol, may be provided in other services where a conventional condensible blowdown drum would not be acceptable (e.g., due to effluent water pollution considerations). Examples of such cases are methyl ethyl ketone (MEK) and dimethyl formamide (DMF). A suitable absorbing material is specified (e.g., a lube oil stock for MEK water for DMF), and the design must include consideration of maximum permissible operating temperatures to prevent excessive vapor evolution or the boiling of water. 

Liquid hydrocarbons accumulated in non-condensible blowdown drums, originating from safety valves, closed drain headers, knockout drum drainage, etc. Facilities are normally provided at the drum for weathering volatile liquids and cooling hot liquids before disposal. 

As an alternative to special pressure slop storage, the necessary holdup may be provided in a non-condensible blowdown drum. 

General In comparison with design information on blowdown drums and cyclone separators, there is very httle information in the open technical hterature on the design of quench tanks in the Chernies industry. What is available deSs with the design of quench tanks (Sso called suppression pools) for condensation of steam or steam-water mixtures from nuclear reactor safety vSves. Information and criteria from quench tanks in the nuclear industry can be used for the design of quench tanks in the chemicS industry. There have been sev-... 

Conventional Flare System - The majority of pressure relief valve discharges which must be routed to a closed system are manifolded into a conventional blowdown drum and flare system. The blowdown drum serves to separate liquid and vapor so that the vapor portion can be safely flared, and the separated liquid is pumped to appropriate disposal facilities. The blowdown drum may be of the condensible or noncondensible type, according to the characteristics of the streams entering the system. Selection criteria, as well as the design basis for each type of blowdown drum, are detailed later in this volume. The design of flares, including seal drums and other means of flashback protection, is described later. 

It is important to note that even if the blowdown is effective in disengaging liquid and vapor, further condensation could occur downstream especially if the vented vapor exits the drum at a temperature above ambient conditions. A proportion of such condensible materials in the blowdown drum vapor release may condense as a result of cooling in the flare header and contact with seal water, and then disengage in the flare seal drum while condensible vapors which are not condensed out at this stage may condense in the flare stack or its inlet line, thus creating the potential for hazardous fallout of burning liquid from the flare. Condensed hydrocarbon in the seal drum can be entrained out with the... 

Lx)cate the blowdown drum (when the non-condensible type is used) at a minimum permissible spacing from the flare, to minimize condensation in the flare header. 

Large condensing loads, if handled on a steady state basis, result in appreciable cooling water and blowdown drum capacity requirements. These loads may be reduced, however, by the use of unsteady state condensing, e.g., by a worm cooler. 

The first vessel in the blowdown system is therefore an acid-hydrocarbon separator. This drum is provided with a pump to transfer disengaged acid to the spent acid tank. Disengaged liquid hydrocarbon is preferably pumped back to the process, or to slop storage or a regular non-condensible lowdown drum. The vented vapor stream from the acid-hydrocarbon separator is bubbled through a layer of caustic soda solution in a neutralizing drum and is then routed to the flare header. To avoid corrosion in the special acid blowdown system, no releases which may contain water or alkaline solutions are routed into it. 

It is important to note that in some installations where local pollution regulations would not permit venting a condensible blowdown tank in toxic service to the atmosphere, a pressure drum or sphere, vented to a flare, may be necessary. 

Y-Leg Seal - The Y-leg seal, which is illustrated in Figure 8, is used for elevated flares in applications where there is no possibility, under any process or ambient conditions, of entrainment or condensation of flammable liquids in the section of the flare header between the blowdown drum and the flare. It is assumed that the blowdown drum is adequately designed to minimize entrainment. 

A blowdown drum was taken out of service and isolated. The drain line was removed and a steam lance inserted to sweeten the tank. The condensate ran out of the same opening. 

Blowdown systems utilize a series of flash drums and condensers to separate the blowdown into its vapor and liquid components. The liquid is typically composed of mixtures of water and hydrocarbons containing sulfides, ammonia, and other contaminants, which are sent to the wastewater treatment plant. 

Flash steam recovery might also feature. Condensate or blowdown is fed to the flash drum, as illustrated in Figure 23.26. A material balance gives ... 

Fig. 1. ASPEN-Plus PFD of carbonic acid pretreatment process as analyzed in this study. Bl, pretreatment reactor (Rstoic) B2, screw mixer B3, blowdown tank and screw conveyor B4, slurrying tank and tank agitator B5, cooler B6, reflux drum and condenser B7, feed pump B8, in-line C02 mixer B9, heater BIO, pneumapress filter Bll, heat exchanger B12, loading pump B13, C02 compressor B14, primary filtrate pump.

Relief line headers, individual relief lines, blowdown lines and flare lines should be self-draining from all relief valve outlets to the knock-out drum, flare stack or a point at the plant limit. A pocketed relief line system is more expensive, because usually an extra condensate pot is required with instruments, valves and pumps. To eliminate... 

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. 

The steam flash drum is a device for steam recovery. Flash steam occurs at the drum where steam condensate or boiler blowdown experiences a drop in pressure causing some of the condensate or boiler blowdown to evaporate forming steam and thus produces steam at the lower pressure (Figure 15.11). For low-pressure condensate, flash steam is negligible and thus it is not worth to recover. However, for medium-and high-pressure condensate, it is important to recover flash steam. 

For Steam Recovery from Blowdown A flash drum eould be used to recover steam firom boiler blowdown or high-pressure condensate. In the former case, the recovered LP steam (Wp ) comes from the overhead of the drum while the bottom is sent to the sewer ... 

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