NO342799B1 - Sequential washing tower for exhaust gases - Google Patents

Abstract

Sequential washing tower is a device / method for washing out oil, particles and noxious gases (eg SO2) from exhaust gas using a vertical co-stream washing scrubber which enables high vertical gas velocities without the risk of accumulation of water. The washcloth is a vertical co-stream washing system where each sequence consists of adding water, separating out and removing most of the added water, before adding new water in the next sequence. The tower is equipped with several nozzle sets (2,4) and one or more parallel fixed spirals (8), which cause rotating flow in the tower, where the added washing water is discharged outward and collected by several vertically mounted collection devices / rails (3, 7). Collected wash water towards the end can be reused at the beginning of the process to streamline wash water consumption, as well as enable the addition of new water towards the end of the process without increasing total water volume. Areas of "grating / gasket" can be arranged directly downstream of each nozzle set to increase the "gas absorption surface" of the water.

Description

Background

The present invention relates to a sequential washing tower for washing exhaust gases. The invention relates in particular to a device and a method for washing out oil, particles and harmful gases (e.g. SO2) from exhaust gas by using a vertical washing tower (scrubber) where the washing is based on several integrated washing sequences/sections in series.

Washing systems are very relevant in connection with IMO, MARPOL legislation Annex VI, which sets requirements for S02 emissions for boats in international and ECA waters, and where exhaust washing has been allowed as an approved secondary solution.

Prior art

Most liquid-based washing systems used today are based on counter-current washing where gas is fed into the bottom of a washing tower and where water is added in the opposite direction and flows against the gas flow, often through a layer of packing rings. This provides good utilization of the water as the fresh water meets the gas at the end of the washing process. The problem with the solution is that the gas velocity in the tower must be limited to prevent water from being dragged along with the gas, thus creating unstable conditions in the washing tower. This results in large dimensions of the washing towers with associated problems related to weight, placement on board "existing" ships, etc.

Publication GB 1261199 Al, describes such a solution where water/chemicals are added upstream and in several stages, but are taken out again collectively/countercurrently and thus result in a limited speed of 0.75-2.55 m/s.

There are also co-flow systems in use (high gas velocity / less weight), but the problem surrounding these is that large amounts of water must be added towards the end of the washing process to achieve cleaning requirements, requirements for S02 emissions, which leads to unnecessarily large water consumption and associated problems related to power needs for e.g. water pumps, as well as problems around water purification systems. Chemical compounds (e.g. NAOH) can be added in the washing process to reduce water consumption somewhat, but this increases costs due to costs related to chemical consumption. High gas velocity generally results in less tower volume than low-velocity countercurrent washing systems, and correspondingly lower costs for building and installing the unit.

The publication EP 1720633 B1 describes a countercurrent scrubber where water is added countercurrently and taken out countercurrently. The design enables the reuse of water, but due to the counterflow principle does not improve the cleaning when water is reused.

The publication SU 1196022 Al describes a scrubber where exhaust gas is introduced into the top of the scrubber, where water is added in several stages (without nozzles) and where internal devices create turbulence and mixing areas for gas and water.

The publication KR 2002/0017738 A describes a horizontal co-current scrubber where water is added via a grid and taken out again collected at the bottom. The design is not stepwise or sequential and does not enable the withdrawal or reuse of water.

The publication KR 2002/0013948 A a counterflow dust separator. It is not high velocity and does not show a co-current washing tower with staged water withdrawal.

Brief description of the invention

One purpose of the present invention is to reduce the consumption of wash water in co-flow wash towers.

Another purpose of the present invention is to enable high gas velocity in a washing tower without the risk of accumulation of water. High gas velocity generally results in less tower volume than low-velocity countercurrent washing systems, and correspondingly lower costs for building and installing the unit.

A third purpose of the present invention is to reduce the amount of water for waste treatment.

A fourth purpose of the present invention is to make it possible for the water purification process before discharge to be scaled down significantly.

A fifth purpose of the present invention is to increase the absorbent surface of the exhaust gas in the washing tower.

The present invention is determined by the independent claims, while the non-independent claims show other embodiments of the invention.

The present invention comprises a sequential washing tower for washing out oil, particles and harmful gases from exhaust gas, where the washing tower comprises an outer vertical tube and an inner vertical tube, where the inner vertical tube is arranged in the center of the washing tower, an inlet for exhaust gas in a lower part, an outlet for washed exhaust gas in an upper part, two or more sets of nozzles for adding water to the washing tower, two or more collectors for withdrawing washing water, one or more fixed parallel spirals arranged between said outer and inner tubes, where the spiral causing rotating upward co-current flow of the mixture of exhaust gas and water through the scrubber tower. Furthermore, the washing tower is divided into two or more sections, where each section comprises a nozzle set for adding and mixing water with the exhaust gas and a subsequent collector for extracting most of the added water, and where the collector in at least one subsequent section comprises a collection pipe for re-injection of the withdrawn water in a lower preceding section.

The sequential washing tower according to the present invention consists of a vertical co-flow washing system consisting of several sections, where each section/sequence involves adding water, separating out and removing most of the added water, before new water is added in the next section/sequence. Water is removed by rotation and internal water collectors, and this enables high gas velocity through the tower without the risk of water accumulation. Removed water from a section/sequence higher up in the tower can be re-injected into a preceding section/sequence in a lower part of the tower by means of a drop height and a water trap, and in this way slightly contaminated water from the upper part is used as wash water in a lower more contaminated part earlier in the washing process. Dividing the washing process into several sections/sequences/steps also enables the separation of highly polluted washing water from less polluted water, which also simplifies water treatment, as well as enabling the addition of clean water towards the end of the process without increasing the total amount of washing water. Inner attachment tubes for spirals are used as a "bypass" of the washing process if problems arise in the nozzle/washing area itself, by means of a simple safety valve / device mounted on top of the inner tube.

The sequential washing tower can also have collection angles, outlets and water flow from the upper part via water trap to lower parts where the water is re-injected / distributed using low-pressure nozzles or other distribution device.

The present invention further comprises a method for washing out oil, particles and harmful gases from exhaust gas using the sequential washing tower.

The procedure includes:

a) to add new water in a subsequent section along with the exhaust gas from a lower preceding section via a subsequent nozzle set in said subsequent section,

b) mixing the new water with the exhaust gas from the lower preceding section,

c) withdrawing and removing most of the added water by means of the collector in the same subsequent

section,

d) to re-inject the extracted water from the collector in a previous lower section via the nozzle set downstream of the gas, e) to repeat withdrawal and re-injection of the water from an upper section to a lower section, so that extracted water from the upper section can be added to a previous lower section .

Brief description of the figures

Figure 1 shows a sequential washing tower according to the present invention.

Figure 2 shows a cross-section of a sequential washing tower indicated in Figures 1 and 3.

Figure 3 shows a sequential washing tower according to the present invention.

Detailed description

Figures 1 and 3 show a sequential washing tower which is arranged with one or more fixed spirals arranged in parallel extending from the lower part to the upper part of the tower. The spirals are attached to an inner pipe 9 in the center of the washing tower, and this pipe is used as a "bypass" for exhaust gas if a problem arises in the washing area itself. The exhaust gas is introduced into the lower part via scrubber intake 10 and taken out in the upper part, via scrubber outlet 11. Water is added via nozzle sets located in upper 4 and lower part 1 and/or between upper and lower part. Incoming gas is set in rotation due to the fixed spirals 8.

The water coming from the nozzle sets mixes with the gas stream 5, and a grid or layer of "packing material" 2,6 can be arranged downstream of the nozzle sets to increase the absorbent surface. Figure 2 shows a cross-section of Figure 1, and shows that the water from the nozzle sets is transported with the gas in the current and is flung out against the wall due to the rotational movement, and is taken out of the tower via internal vertical angles/collectors 3,7, and is led out via collecting pipes for each collects section/step. As shown in Figures 1 and 3, the water that is taken out is recycled to the nozzle sets further down as needed using a drop height and possibly a water trap. Relatively clean water taken from the end of the washing process can in this way be re-injected to the beginning of the washing process. This recycling of the water means that the consumption of washing water and the amount of water for waste treatment is reduced considerably, and that the water purification process before discharge is scaled down significantly.

The tower can consist of several such washing sections arranged in series, to increase the degree of cleaning.

The inner tube is used as a "bypass" of the washing area, using a simple valve device mounted on top of the inner tube which closes due to its own weight or with the help of a spring. The current valve device is designed as a simple combined self-opening safety valve with the possibility of manual operation, which opens when the pressure in the inner pipe exceeds a predetermined value in relation to the outer pipe.

Claims (7)

1. A sequential washing tower for washing out oil, particles and harmful gases from exhaust gas, characterized in that the washing tower comprises - an outer vertical tube and an inner vertical tube (9), where the inner vertical tube (9) is arranged in the center of the washing tower, - an inlet (10) for exhaust gas in a lower part, - an outlet (11) for washed exhaust gas in an upper part, - two or more nozzle sets (1,4) for adding water to the washing tower, - two or more collectors (3 ,7) for the extraction of washing water, - one or more fixed parallel spirals (8) arranged between the said outer and inner pipe (9), where the spiral causes a rotating upward co-current flow of the mixture of exhaust gas and water through the washing tower, where the washing tower is divided into two or more sections, where each section comprises a nozzle set (1,4) for adding and mixing water with the exhaust gas and a subsequent collector (3,7) for extracting most of the added water, and where the collector (7) in at least one subsequent section comprises a collecting pipe for re-injection of the withdrawn water in a lower preceding section. 2. Sequential wash tower according to claim 1, characterized in that it comprises more than two sections which enable the extraction of wash water of different purity from different sections, and enable the re-injection of wash water from at least one subsequent upper section to the preceding lower section by means of drop height and a possible water lock. 3. Sequential washing tower according to claim 1 or 2, characterized in that the collector (3,7) consists of vertical angles. 4. Sequential washing tower according to any one of claims 1 to 3, characterized by further comprising a mesh, perforated plate or packing rings (2,6) arranged downstream of one of said nozzle sets (1,4) to increase the absorbent surface for better gas absorption. 5. Sequential washing tower according to any one of claims 1 to 4, characterized in that the inner pipe (9) comprises an opening and closing device at the upper end so that the pipe can be used as a bypass for exhaust gas. 6. Method for washing out oil, particles and harmful gases from exhaust gas using a sequential washing tower according to any one of claims 1 to 5, characterized in that the method comprises: a) adding new water in a subsequent section with the flow of the exhaust gas from a lower preceding section via subsequent nozzle set (4) in said subsequent section, b) to mix the new water with the exhaust gas from the lower preceding section, c) to take out and remove most of the added water by means of the collector (7) in the same subsequent section section, d) to re-inject the extracted water from the collector (7) into a previously lower section via the nozzle set (1) downstream of the gas, e) to repeat withdrawal and re-injection of the water from an upper section to a lower section, so that extracted water from the upper section a previous lower section can be added. 7. The method according to claim 6, where the washing tower consists of more than two sections, and characterized in that steps a), b), c) and d) of the method are repeated for at least two consecutive sections in the washing tower.