Riser tubes separators

From here the water mixture rises through the water-wall tubes (generator tubes) that constitute the furnace membrane where steam is generated (primarily by radiant energy transfer). The steam-BW mixture is collected in top water-wall headers and conducted through risers (riser tubes) back to the top drum, where the saturated steam separates from the water at the steam-water interface. 

Figure 8.1 Internal-loop airlift bioreactor with (a) a baffle separating the riser and downcomer, (b) a continuous draught tube separating the riser and downcomer, and (c) a sectioned draught tube separating the riser and downcomer.

Steam-water mixture flow in the riser tubes 8 - Preliminary separation at the ontlet from the riser tnbes... 

The dissipated energy due to flow resistance and turbulence F consists of four parts the energy consumption in the riser, that in the separator tubes, X that in the down-comer, and that due to the flow direction changes of the U-bending channel at the top and bottom of the reactor,/,. Therefore, F can be written as ... 

In the Fig.4, it can be seen that the gas hold-up in both riser and downcomer decreases with increasing the draft-tube horn-mouth diameter and approaches the maximum when the draft-tube hom-mouth diameter is 1.05m. However, due to the gas hold-up decreases more in the downcomer, the gas hold-up difference between the downcomer and the riser increases. Therefore, the apparent density difference between the riser and the downcomer enhances, causing higher liquid superficial velocity in the downcomer and in the riser With increasing the hom-mouth diameter. Fig.5 also shows that the existence of hom-mouth promotes the ability to separate gas from liquid and decreases the amount of gas entrained into the downcomer. 

Figure 7.11b shows an EL airlift reactor, in schematic form. Here, the downcomer is a separate vertical tube that is usually smaller in diameter than the riser, and is connected to the riser by pipes at the top and bottom, thus forming a circuit for liquid circulation. The liquid entering the downcomer tube is almost completely degassed at the top. The liquid circulation rate can be controlled by a valve on the connecting pipe at the bottom. One advantage of the EL airlift reactor is that an efficient heat exchanger can easily be installed on the hquid loop hne. 

The main variable is Fr, which represents the influence of gas input rate (and also the energy input rate). Its effect on holdup is much stronger in the downcomer than in the riser, and the balance between the two gives an exponent of almost 1 (1.05) for the total holdup. Interestingly, the behavior of holdup in the gas separator is very close to that of total holdup. As draft-tube bottom clearance ct b increases. Or decreases. ... 

Figure 7.11b shows an EL airlift reactor, in schematic form. Here, the downcomer is a separate vertical tube that is usually smaller in diameter than the riser, and is connected to the riser by pipes at the top and bottom, thus forming a circuit for... 

The safety vessel is surrounded by an additional vessel of the emergency cooldown system. A shell is installed in the gap between these vessels. This shell separates it into riser and downcomer channels where natural circulation of atmospheric air takes place, see Fig. XVI-2. The shell separating the gap into channels has very high thermal resistance. The channels are connected with the exhaust and input tubes. Nominal characteristics of the emergency cooldown system are given in Table XVI-9. 

In airlift bioreactors the fluid volume of the vessel is divided into two interconnected zones by means of a baffle or draft-tube (Fig. 5). Only one of these zones is sparged with air or other gas. The sparged zone is known as the riser the zone that receives no gas is the downcomer (Fig. 5a-c). The bulk density of the gas-liquid dispersion in the gas-sparged riser tends to be less than the bulk density in the downcomer consequently, the dispersion flows up in the riser zone and downflow occurs in the downcomer. Sometimes the riser and the downcomer are two separate vertical pipes that are interconnected at the top and the bottom to form an external circulation loop (Fig. 5c). External-loop airlift reactors are less common in commercial processes compared to the internal-loop designs (Fig. 5a, b). The internal-loop configuration may be either a concentric draft-tube device or an split-cylinder (Fig. 5a, b). Airlift reactors have been successfully employed in nearly every kind of bioprocess—bacterial and yeast culture, fermentations of mycelial fungi, animal and plant cell culture, immobilized enzyme and cell biocatalysis, culture of microalgae, and wastewater treatment. 

It consists of an upper drum (steam drum) and a lower drum (mud drum) connected by tubes. The steam generating tubes are located in the hottest area of the boiler and they are called risers. The combustion gases first pass here. The steam-water mixture is carried to the steam drum where steam is separated from water. Water flows from the steam drum, through the cooler tubes to the lower drum (mud drum). These tubes are named as downcomers (Fig. 11.5). The mud drum separates suspended solids and sludge from the water. 

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