Venting reboiler

Due to high liquid head, this vent is ineffective for venting reboiler... 

Type 77 units are the condenser and reboiler designs. One side is spiral flow and the other side is in cross flow. These SHEs provide veiy stable designs for vacuum condensing and reboiling seiwices. A SHE can be fitted with special mounting connec tions for refliix-type vent-condenser apphcations. The vertically mounted SHE directly attaches on the column or tank. 

The top pressure controller varies the level of liquid in the condenser, so it, like the reboiler, must have extra surface for the derating required for control. Many other control methods also require some control surface. If noncondensibles are present, a vent should be provided. Otherwise, they collect at the liquid seal. With large amounts of noncondensibles, another type of system should be considered. 

Pressures above atmospheric in the reboiler can significantly reduce lean glycol concentration and dehydration effieiency. The still column should be adequately vented and the packing replaced periodically to prevent excess back pressure on the reboiler. 

The pump gas can be used to fuel the reboiler. The amount of pump gas is normally close to balancing the reboiler fuel gas requirements. The pump gas can also be routed to the facility fuel gas system or to a low-pressure system for compression and sales. If it is not recovered in one of these ways and is just vented locally, the cost of using this type of pump can be very high. 

In large and extensive industrial process plants, it is not unusual to find unvented condensate receivers or reboilers at the end of a long steam-condensate line. These vessels tend to act as collection and storage points for carbon dioxide, which may redissolve in condensate. These satellite stations should be vented and receive an amine booster feed. 

One important feature of Fig. 8.6 is the condensate drum balance line. Note, that this line is connected below the channel head pass partition baffle. This ensures that the pressure in the channel head, below the pass partition baffle, and the pressure in the condensate drum, are the same. If these two pressures are not identical, then the level in the condensate drum cannot represent the level in the channel head. For this reason, never connect the condensate drum vapor space to either the steam supply line or the top vent of the reboiler s channel head. 

Venting the channel head through the balance line shown in Fig. 8.6 will prevent an excessive accumulation of C02. This is done by continuous venting from the top of the condensate drum. For every 10,000 lb/h of steam flow, vent off 50 lb/h of vapor through a restriction orifice, placed in the condensate drum vent. This is usually cheaper than controlling reboiler steam-side corrosion, with neutralizing chemicals. 

Since helium and neon have boiling points considerably below that of nitrogen, these gases will collect on the nitrogen side of the condenser-reboiler associated with the double-column air separation system. Recovery of these gases is accomplished by periodic venting of a small portion of the gas from the dome of the condenser and transfer to a small condenser-rectifier refrigerated with... 

Figure 3.6a shows how costs for a new distillation system vary with the reflux ratio. It expresses the capital cost as an annual cost. This can be achieved hy dividing the capital cost by the expected payout period. A discounted cash flow (DCF) analysis is used for estimating this payout period. The capital cost shonld include the costs of auxiliaries (reboiler, condenser, vacuum equipment, pumps, piping in many cases, costs of vent systems, coolant, and heating medium handling equipment are also affected). The operating costs should include reboiler... 

Warm vapors sometimes condense inside closed vessels the resulting may collapse the vessel. Such incidents have occurred when a vessel was purged with steam, then closed in without venting. Similarly, a distillation column may go to vacuum if reboil fails but condensing continues. 

The first stage consists of five parallel groups of two series-connected towers, of which one group, lA and IB, are shown in Fig. 13.3. Feed for each lA tower consists of condensate from the reboiler of the associated IB tower. Feed is introduced at the top of the lA tower. Stripped vapor from the top plate is condensed in a barometric condenser, vented to a steam qector that maintains a pressure of from SO to 90 Torr at the top of the tower. 

Most of the water at the bottom of IB, now enriched to 0.117 a/o deuterium, is converted to vapor in the reboiler and returned to IB, but around 12 percent is pumped ahead to the top of 2A. Vapor from the top of 2A is condensed in a condenser refrigerated with ammonia, to prevent loss of the now valuable water. This condenser is also vented to a steam qector, which maintains a pressure of 130 Ton. 

Vapor disentrainment is not required in a sump or draw pan used exclusively to feed a thermosiphon reboiler, because the reboiler can handle some vapor bubbles in its liquid supply. It is important to size the reboiler sump for self-venting flow otherwise vapor pockets may choke the reboiler sump. Figure 4.5 can be applied to determine the maximum allowable velocity through the reboiler sump. The pipe diameter on the y axis of the diagram is considered... 

When the bottom sump does not supply liquid to a reboiler (e.g., when a reboiler trapout pan is used, or when the column has a bottom feed and no reboiler), the design in Fig. 4.86 can be used with thermally unstable materials. This arrangement eliminates the need for a surge drum and self-venting lines, and immediately quenches liquid reaching the column base. 

Poor performance can be caused by leaks (e.g., block valves on connecting pipes, vent valves) into or out of the system. The effects are similar to those described in Sec. 13.14. In one case (2066), a column separating propane from butadiene experienced excessive propane in the bottom. The cause was a seal failure on the reboiler pump the pump used propane as seal gas. 

Inerts. Accumulation of inerts can drastically reduce heat transfer, particularly in steam reboilers. Accumulation of acidic or oxidizing inerts such as CO2 is also known to have caused severe corrosion (234, 253, 254). Numerous troublesome case histories of inert accumulation in the heating side of reboilers have been reported (28, 96, 232, 239). Inert venting facilities must be adequate. The following guidelines have recommended for venting inerts (28, 377, 381) ... 

There should be a well-defined flow path to positively guide noncondensables from the reboiler inlet to the vent outlet. If the flow path is defined by baffles, baffle design should ensure adequate sweeping of inerts. 

The vents must be located at the end of the vapor flow path, regardless of where this is located. Figure 15.10a, based on Bell s case history (28), shows a reboiler that performed poorly due to inert accumulation, and where a vent should have been located. 

All vapors to be condensed contain noncondensables. A vapor containing as little as 100 ppm noncondensables can fill a reboiler up with noncondensable gas within less than 10 h if there is no venting (28). 

It is good practice to provide tubesheet vents (134, 254, 358 Fig. 15.106) opposite the top vapor inlet nozzle in a vapor-heated vertical reboiler (condensing on the shell side). This is essential in steam reboilers, where a small steam purge should be continuously vented to atmosphere. Shell corrosion due to CO2 accumulation is known to have occurred in steam reboilers that had no such vent (234, 254). 

Venting inerts from the floating head end of a horizontal reboiler can be difficult. A novel method which successfully accomplished this (232) was installing a 1-in internal pipe that extended a top tube from the channelhead tubesheet to a vent in the channel head (Fig. 15.10c). The top tube was thus converted into a "vent tube. The internal pipe was coupled to the vent from inside the channel head, to permit removal. This technique cured a CO2 corrosion problem attributed to poor venting at the floating head end. 

In steam reboilers, a small atmospheric vent should be provided on top of the condensate drum and always left cracked open (234) (except when steam chest pressure dips below atmospheric). This will... 

Fired reboilers are principally used in refineries. Usually, these are fired with a mixtime of gases vented from various units, supplemented by natural gas. A problem with direct-fired reboilers is variation of heat input due to changes in fuel gas composition. For this reason, it may be unsatisfactory to control the fuel flow rate to the furnace, and heat input control may be necessary. 

Recycle reactants separator (Cg range) Vertical thermosiphon reboiler performed poorly because of inerts accumulation on its condensate side. Venting was inadequate. Ensure adequate venting on reboiler condensate side. 

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