GB1599128A

GB1599128A - Contact apparatus for carrying out heat-and-mass exchange processes

Info

Publication number: GB1599128A
Application number: GB12180/78A
Authority: GB
Original assignee: MOSKOV INST KHIM MASHINOSTR
Current assignee: MOSKOV INST KHIM MASHINOSTR
Priority date: 1978-03-29
Filing date: 1978-03-29
Publication date: 1981-09-30
Also published as: DE2820200C2; FR2426482A1; FR2426482B1; DE2820200A1

Description

(54) IMPROVEMENTS IN OR RELATING TO A CONTACT APPARATUS FOR CARRYING OUT HEAT-AND-MASS EXCHANGE PROCESSES (71) We, MOSKOVSKY INSTITUT KHIMICHESKOGO MASHINOSTROENIA a Corporation organised and existing under the laws of the U.S.S.R., of ulitsa K.Marxa 21/4.

Moscow, Union of Soviet Socialist Republics, do hereby declare the invention, for which we pray that a patent may be granted to us. and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates generally to apparatus for carrying out heat-and-mass exchange processes in a gas or vapour-liquid system and more specifically, to contact apparatus of this tvpe.

The invention can find most utility when applied in fractionating and absorption columns for continuous processing under heavv loads in terms of liquid processed, e.g., for purifying converted gas from carbon monoxide and dioxide by various absorbents, as well as for processes for absorbing nitrogen oxides by water in producing weak nitric acid.

One of the main trends in operating modern apparatus for carrying out heat-and-mass exchange processes proceeding between gas or vapour and liquid, resides in the use of higher pressures in such apparatus which results in higher loads thereupon in terms of liquid processed. That is why up-to-date apparatus for carrymg out heat-and-mass exchange processes should meet the requirements of ensuring higher liquid throughput capacity.

It is an object of the present invention to provide a contact apparatus for carrying out heat-and-mass exchange processes, having high liquid throughput capacity.

It is another object of the present invention to increase the efficiency of a contact apparatus and extend the range of stable operation thereof.

According to the invention. there is provided contact apparatus for carrying out continuous heat-and-mass exchange processes in a gas or vapour-liquid system, comprising a duct for the passage therethrough of the gas or vapour and the liquid and a perforated tray extending across the duct and having ports adapted for the passage of gas or vapour and having at least one liquid overflow device formed by two spaced coaxial shells, a top one of the two spaced coaxial shells in the direction of the flow of liquid, partly enclosing the other, bottom. shell and comprising two shell pieces interconnected through a guide member, the bottom shell piece of the top shell having a smaller flow passage area than the top shell piece of the top shell, the upper edge of the guide member being situated above the upper end of the bottom shell: and two baffles, of which one is located under and spaced from a lower end of the bottom shell piece of the top shell. and the other is situated under and spaced from a lower end of the bottom shell. the baffles being so arranged as in use to receive liquid from the bottom shell piece and the bottom shell respectively and to direct the liquid in respective directions transverse to the axis ot the top and bottom shells.

In such a contact apparatus. the liquid throughput capacity of the contact apparatus is enhanced due to provision of an increased deaeration surface area which results in a larger flow passage area of the liquid overflow device and reduced rate of ascent of deaeration gas bubbles. the latter preventing the blockage of the overflow device passage area by the deaeration gas.

A satisfactory deaeration of liquid in the overflow device leads to a better liquid escape from the device. whereby stable liquid films are formed in the intertray column space, which are in contact with the ascending vapour or gas, thus adding to the efficiency of the contact apparatus as a whole.

Since the constructional arrangement of the contact apparatus according to the invention increases a maximum liquid throughput capacity thereof due to a better deaeration and improved liquid receiving conditions where the liquid feeds onto subjacent perforated bases, this provides in an increased range of stable operation and efficiency of the contact apparatus.

Other objects and advantages of the present invention will become more obvious from a consideration of the following specific embodiment thereof to be taken with reference to the accompanying drawings, wherein: Figure 1 is a schematic longitudinal cross-section of a contact apparatus, according to the invention, featuring one overflow device; Figure 2 is a plan view of a contact apparatus. according to the invention, incorporating nine overflow devices made as cylindrical sleeves, ports for gas or vapour to pass being omitted.

Figure 3 is a contact apparatus, according to the invention, including partition plates and receiving troughs; Figure 4 is a plan view of a contact device, according to the invention, featuring three overflow devices made as rectangular cross-section ducts, the ports for gas or vapour being omitted; and Figure 5 is a scaled-up view of a part of a contact apparatus, according to the invention.

The contact apparatus for carrying out continuous heat-and-mass exchange processes in a gas or vapour-and-liquid system, such as the absorption of nitrogen oxides with water, comprises a perforated tray I (Figure 1) accommodated in a duct 2 and provided with ports 3 for nitrous gas, for example. to pass through the base and with at least one liquid overflow device 4.

The overflow device 4 is mounted on the tray 1 and includes two spaced coaxial shells 5 and 6. The top shell 5, in the direction of the flow of liquid, partly encloses the bottom shell 6, and is composed of two shell pieces 7 and 8 coaxial with each other and interconnected through a guide member 9. The bottom shell piece 8 has smaller flow passage area than the top shell piece 7. The lower edge 9a of the guide member 9 is situated above the upper end 6a of the bottom shell 6. In addition, the contact apparatus incorporates two baffle 10 and 11. The baffle 10 has a clearance 12 with respect to the lower end 6b of the bottom shell 6, while the baffle 11 has a clearance 13 with the lower end 8a of the bottom shell piece 8. The shell pieces 7 and 8 as well as the shell 6 have the shape of cylindrical sleeves. When more than one overflow device 4 is located on the tray 1, they are isolated from one another by partition plates 14 for guiding the flow of liquid. The perforated tray 1 has a receiving trough 15 (Figure 3) spaced equidistantly between adjacent overflow devices 4.

The contact apparatus for absorption of nitrogen oxides operates as follows: The liquid, viz; water or a solution of weak nitric acid, located on the perforated tray 1 (Figure 1). flows towards the overflow device 4, whereas the gas, viz., nitrogen oxides, while passing through the ports 3, interacts with the liquid to form a double-phase flow.

Having contacted the liquid, the gas ascends to a superjacent contact apparatus, whereas the liquid after having reached the upper end of the top shell pieces 7, enters the overflow device 4, wherein it is directed by the guide member 9 to flow into the bottom shell 6, wherefrom the liquid is directed by the baffle 10 in a direction transverse to the axis of the top and bottom shells 5. 6 to escape as a flat stream or film into the intertray column space.

As the load in terms of liquid rises due to a raised liquid level in the bottom shell 6. and upon the liquid reaching the upper end 6a. the liquid flows over the upper end 6a into the space between the walls of the bottom shell 6 and of the bottom shell piece 8, whereupon the liquid flows through the clearance 13 and is directed by the baffle 11 transverse to the axis of the top and bottom shells 5, 6 into the intertray space as a flat stream. Thus, two parallel flows of liquid are established in the intertray space, which interact with the gas ascending from a subjacent contact apparatus.

On reaching the column duct 2 (Figures 2, 3, 4) or the partition plates 14, the liquid runs down onto the tray 1 or into the throughs 15 (Figure 3) which damps the velocity head of the flow of liquid and provides a smooth passage of the liquid onto the base 1, as well as contributing to a better redistribution of the liquid over the surface of the tray 1. Damping of the liquid flow velocity head and a smooth passage of the liquid flow onto the tray 1 result in higher operational limit of the contact apparatus in terms of liquid flow and in an extended range of efficient operation.

Provision of the overflow device formed by two shells 5 and 6, with the shell 5, in turn, composed of two shell pieces 7 and 8 interconnected through the guide member 9 establishes favourable conditions for a better deaeration of the liquid which makes it possible to increase the liquid throughput capacity of the contact apparatus and define a stable escape of the liquid from the gaps 12 and 13.

To attain a higher liquid throughput capacity of the contact apparatus in comparison with apparatus having overflow devices made in the form of cylindrical sleeves having the same area. the shell pieces 7 and 8 and the bottom shell 6 may, as seen in Figure 4, be shaped as rectangular cross-section ducts.

In a further modification of the apparatus of Figure 1, the baffle 11 (Figure 5) may be spaced from the outer wall of the bottom shell 6 to provide a clearance 16 between the baffle 11 and the bottom shell 6. the amount of the clearance 16 being so selected as to allow the liquid to pass to the bottom baffle 10.

The bottom shell 6 has ports 17 for the passage of liquid, said ports being in a part of the wall of the shell 6 above the lower end 8a of the shell piece 8.

The modified apparatus of Figure 5 operates in a way similar to that described above with reference to Figure 1, with the exception that the flow of liquid passing through the space between the wall of the bottom shell piece 8 and that of the bottom shell 6 is split into two portions, of which one escapes from the clearance 13, while the other passes through the clearance 16 to the baffle 10, thus adding to the liquid throughput capacity of the apparatus and the intensity of disintegration of the lower flow of liquid and, correspondingly, to the efficiency of the heat-and-mass transfer. The ports 17 in the bottom shell 6 establish a hydraulic lock above the clearance 13, which prevents ingress of gas through said clearance, thus preventing the overflow device from being blocked-up by the gas flow.

The contact apparatus according to the present invention. made use of an absorber for purifying a nitrogen-hydrogen mixture from carbon dioxide with a monoethanolamine solution. involved in ammonia production process, provided for absorber operation at a liquid load from 5 to 150 m3/m2 per hour and a gas flow velocity effective in the absorber cross-sectional area as calculated for the value f, = WVp k fl5 ux to be equal to 3.0 where W is the gas flow velocity in the absorber.

p is the gas density in the absorber.

WHAT WE CLAIM IS: 1. Contact apparatus for carrying out continuous heat-and-mass exchange processes in a gas or vapour-liquid system, comprising a duct for the passage therethrough of the gas or vapour and the liquid. a perforated tray extending across the duct and having ports for the passage of gas or vapour and having at least one liquid overflow device formed by two spaced coaxial shells, a top one of the two spaced coaxial shells, in the direction of the flow of liquid, partly enclosing the other bottom shell and comprising two shell pieces interconnected through a guide member, the bottom shell piece of the top shell having a smaller flow passage area than the top shell piece of the top shell, the upper edge of the guide member being situated above the upper end of the bottom shell, and two baffles, of which one is located under and spaced from a lower end of the bottom shell piece of the top shell, and the other is situated under and spaced from a lower end of the bottom shell the baffles being so arranged as in use to receive liquid from the bottom shell piece and the bottom shell respectively and to direct the liquid in respective directions transverse to the axis of the top and bottom shells.

2. Contact apparatus as claimed in claim 1. wherein the top shell piece, the bottom shell piece and the bottom shell each have the shape of a cylindrical sleeve.

3. Contact apparatus as claimed in Claim 1, wherein the top shell piece, the bottom shell piece and the bottom shell each have the shape of a rectangular cross-section duct.

4. Contact apparatus as claimed in Claims 1. 2 or 3, wherein the baffle provided under the lower end of the bottom shell piece surrounds the bottom shell but is spaced therefrom to provide a clearance between said baffle and and an outer wall of the bottom shell, said clearance being provided below the lower end of the bottom shell piece.

5. Contact apparatus as claimed in Claim 1 when dependent on Claims 2 and 4, or in Claim 1 when dependent on Claims 3 and 4. wherein the bottom shell has a number of ports for the passage of liquid. said ports being provided in a part of the wall of said bottom shell which is above the lower end of the bottom shell piece.

6. Contact apparatus as claimed in Claim 1, provided with at least two overflow devices, wherein the perforated tray has receiving troughs, each of which is spaced equidistantly between two adjacent overflow devices, is located below the partition plate and subdivides the perforated tray into compartments, each compartment accommodating an overflow device.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. area. the shell pieces 7 and 8 and the bottom shell 6 may, as seen in Figure 4, be shaped as rectangular cross-section ducts. In a further modification of the apparatus of Figure 1, the baffle 11 (Figure 5) may be spaced from the outer wall of the bottom shell 6 to provide a clearance 16 between the baffle 11 and the bottom shell 6. the amount of the clearance 16 being so selected as to allow the liquid to pass to the bottom baffle 10. The bottom shell 6 has ports 17 for the passage of liquid, said ports being in a part of the wall of the shell 6 above the lower end 8a of the shell piece 8. The modified apparatus of Figure 5 operates in a way similar to that described above with reference to Figure 1, with the exception that the flow of liquid passing through the space between the wall of the bottom shell piece 8 and that of the bottom shell 6 is split into two portions, of which one escapes from the clearance 13, while the other passes through the clearance 16 to the baffle 10, thus adding to the liquid throughput capacity of the apparatus and the intensity of disintegration of the lower flow of liquid and, correspondingly, to the efficiency of the heat-and-mass transfer. The ports 17 in the bottom shell 6 establish a hydraulic lock above the clearance 13, which prevents ingress of gas through said clearance, thus preventing the overflow device from being blocked-up by the gas flow. The contact apparatus according to the present invention. made use of an absorber for purifying a nitrogen-hydrogen mixture from carbon dioxide with a monoethanolamine solution. involved in ammonia production process, provided for absorber operation at a liquid load from 5 to 150 m3/m2 per hour and a gas flow velocity effective in the absorber cross-sectional area as calculated for the value f, = WVp k fl5 ux to be equal to 3.0 where W is the gas flow velocity in the absorber. p is the gas density in the absorber. WHAT WE CLAIM IS:

1. Contact apparatus for carrying out continuous heat-and-mass exchange processes in a gas or vapour-liquid system, comprising a duct for the passage therethrough of the gas or vapour and the liquid. a perforated tray extending across the duct and having ports for the passage of gas or vapour and having at least one liquid overflow device formed by two spaced coaxial shells, a top one of the two spaced coaxial shells, in the direction of the flow of liquid, partly enclosing the other bottom shell and comprising two shell pieces interconnected through a guide member, the bottom shell piece of the top shell having a smaller flow passage area than the top shell piece of the top shell, the upper edge of the guide member being situated above the upper end of the bottom shell, and two baffles, of which one is located under and spaced from a lower end of the bottom shell piece of the top shell, and the other is situated under and spaced from a lower end of the bottom shell the baffles being so arranged as in use to receive liquid from the bottom shell piece and the bottom shell respectively and to direct the liquid in respective directions transverse to the axis of the top and bottom shells.

7. Contact apparatus as claimed in any one of Claims 1 to 6 substantially as disclosed in

the description and illustrated in Figures 1 to 5.