Venturi cleaning system with two adjustable venturi grooves

The invention relates to a differential pressure cleaning system consisting of a flow pipe (7) with a throttle (1) and at least one cleaning fluid feed device (14) fitted over the throttle (1) for treating exhaust gases from technical processes which give off mixtures of gases, vapors and dusts. The throttle (1) located in the flow pipe (7) takes the form of an approximately rectangular slot (2) at its narrowest point. A displacement body (3) is arranged downstream of the slot (2), extending over the entire length of the slot and mounted in such a way as to be movable towards and away from the slot (2). This provides two roughly parallel venturi grooves (6) between the walls of the throttle (1) and the outer wall of the displacement body. The cross-sections of these two venturi grooves (6) can be adjusted as desired by moving the displacement body (3). The throttle (1) in the flow pipe (7) is preferably realised by two commercially available transverse pipes (8) displaying a circular cross-section. The flow pipe (7) and the displacement body (3) may also be made of commercially available pipes with a circular cross-section.

The invention relates to a differential pressure cleaning system consisting 
of a flow pipe with a throttle and at least one cleaning fluid feed device 
fitted over the throttle. 
The exhaust gases from technical processes are generally mixtures of gases, 
vapours and dusts. The dust-like, i.e. disperse proportion, can occur in 
the carrier gas in both solid and liquid form. The separation of solid or 
liquid particles, as well as the separation of a gaseous component from 
the gaseous dispersing agent, are part of the processes of mass transfer. 
Acceleration and deceleration of the gas flow and of an injected cleaning 
fluid causes turbulent vortexing of the gas, dust and liquid droplets with 
one another. This results in very rapid wetting of the dust particles and 
accelerates chemical reactions. The energy required for the separation 
process is provided by the flow energy of the gas to be scrubbed. If the 
process involves hot gases, in particular, which must be cooled, 
condensation processes are also used, these being characterized by 
enthalpy reduction and utilisation of the dust particles as condensation 
nuclei. 
Part of the flow energy is lost as a result of the interaction between the 
cleaning fluid and the dispersion agent. The unavoidable occurrence of 
friction in this context leads to the dissipation of energy, i.e. to a 
pressure loss and an additional pressure gradient in the direction of the 
gas flow. 
The energy consumed naturally increases with the difficulty of the mass 
transfer process. Therefore, in the case of high gas-scrubbing demands, 
cleaners are used through which the gas flows at high velocities. 
These wet scrubbers are known as "differential pressure cleaning systems" 
due to the comparatively great pressure differences occurring in them. 
The most commonly, used differential pressure cleaning system is the 
venturi cleaning system, of which numerous designs exist. This type of 
cleaning system is typified by the venturi pipe, where the cleaning fluid 
is injected at low Pressure at the narrowest cross-section, the throttle, 
via an axial injector or via a transverse injector. As a result of the 
intense shearing effect of the gas flow, the liquid particles are torn 
into ultrafine droplets. The high acceleration of the gas in the throttle 
and the resultant high relative velocity between the dust particles and 
the droplets are the reason for the very good separating properties of the 
venturi cleaning system. Depending on the separation performance, the 
pressure loss is between 3,000 and 2,000 pascal. The exact pressure loss 
depends on the gas velocity and the quantity of cleaning fluid injected. 
A venturi cleaning system reacts very strongly to fluctuations in load on 
account of the connection between separation performance and flow 
velocity. This problem is counteracted technically by changing the 
cross-section of the venturi throttle, where the throttle cross-section is 
designed as a rectangular slot and the longitudinal walls are adjustable. 
However, the problem of load fluctuations can also be overcome by sucking 
in secondary air or ambient air. However, both approaches to solving the 
problem of load fluctuations involve an enormous design effort. 
Another type of differential pressure cleaner is the annular gap cleaner. 
In this type of cleaner, the change in cross-section is achieved by 
vertically displacing a conical, centrally-fitted displacement body, such 
as a conical and axially movable adjusting body, which forms an annular 
gap with the housing. The annular gap between the conical displacement 
body and the housing, through which the gas flows, then serves as a mixing 
stage for the cleaning fluid and the gas to be cleaned. On account of the 
relatively small adjustable annular gap, the spraying density and gas 
velocity are extraordinarily high, which is an essential factor in the 
scrubbing process. 
The disadvantage of annular gap cleaners, however, is the extraordinary 
design effort involved, as the conical displacement bodies, in particular, 
are relatively difficult to manufacture and annular gap cleaners require 
more Space than venturi cleaning systems. Furthermore, the separation 
performance of annular gap cleaners is poorer than that of venturi 
cleaning systems, as becomes particularly noticeable when scrubbing gases 
bearing condensation and sublimation dust. 
Therefore, the task of the present invention is to develop a differential 
pressure cleaning system which provides a good separation performance 
without a high pressure loss, i.e. which can be rapidly adjusted to load 
fluctuations, and which can be realised by means of a simple design. 
According to the invention, the task is solved by the fact that the 
throttle located in the flow pipe takes the form of an approximately 
rectangular slot at its narrowest point and that a displacement body is 
arranged downstream of the slot, extending over the entire length of the 
slot and mounted in such a way as to be movable towards and away from the 
slot, which provides two roughly parallel venturi grooves between the 
walls of the throttle and the outer wall of the displacement body, and 
where the cross-sections of these two venturi grooves can be adjusted as 
desired by moving said displacement body. 
By means of this design, it is relatively simple to change the 
cross-section of a conventional flow pipe or venturi pipe in the area of 
the throttle in such a way that two precisely adjustable venturi grooves 
are formed. This has the advantage that load fluctuations can be countered 
very quickly and simply. Furthermore, the displacement body can take a 
very simple form. In principle, any form can be used. 
In order to minimise the design effort, the throttle is preferably formed 
by arranging two transverse pipes in the flow pipe. These transverse 
pipes, which typically display a roughly circular cross-section, like the 
flow pipe, may penetrate the flow pipe either entirely or partially. 
Commercially available tubes may be used in this context, and the 
manufacture of special assemblies is unnecessary. 
The use of such tubes as components also allows inexpensive production in 
the case of differential pressure cleaners which have to be designed for 
high differential pressures. 
In order to achieve the best possible gas flow from the point of view of 
fluid mechanics, a preferred embodiment of the invention displays guide 
plates arranged between the inner wall of the flow pipe and the surface 
areas of the transverse pipes, upstream and/or downstream of the slot. 
The displacement body is preferably of tubular design and displays a 
circular cross-section. The use of such a hollow cylindrical displacement 
body as a component facilitates low-cost production, with commercially 
available pipes again being suitable for use in this context. 
It is, however, also possible to use a displacement body of a different 
design, a solid cylindrical displacement body being particularly worthy of 
consideration in this context. 
The displacement body is expediently positioned with its face ends in 
positive contact with the adjacent inner walls of the flow pipe. 
In a preferred embodiment of the invention, recesses are provided in the 
face ends of the displacement body and matching guide rails are arranged 
on the adjacent inner wall areas of the flow pipe. This feature 
facilitates precise axial displacement of the displacement body and thus 
precise adjustment of the width of the slots of the two venturi grooves. 
In another preferred embodiment, the throttle can be closed completely by 
the displacement body. This allows the differential pressure cleaner to be 
used as a stop valve at the same time, even providing a completely 
gas-tight seal due to the cleaning fluid above the closed displacement 
body. This thus dispenses with the need for gas gate valves. 
Furthermore, the displacement body can be adjustable via a spindle drive 
which can typically be operated manually by a handwheel or similar. 
However, it is also possible for the displacement body to be mechanically 
controlled as a function of the pressure. 
In a preferred embodiment, the flow pipe and/or the transverse pipes and/or 
the displacement body and/or the guide plates are made of 
corrosion-resistant thermoplastic materials, e.g. polypropylene or 
polyvinyl chloride, using available semifinished products. 
It is likewise possible to manufacture the differential pressure cleaner 
from steel or special steel. 
The cleaning fluid is expediently injected by means of at least one swirl 
nozzle. 
The cleaning fluid is preferably injected parallel to the direction of 
flow, although it is feasible for the cleaning fluid to be injected at an 
angle or perpendicular to the direction of flow.

According to the drawing, the differential pressure cleaner comprises a 
flow pipe 7 which, as can be seen from FIG. 3, displays a circular 
cross-section, with a throttle 1 arranged roughly in the centre of the 
differential pressure cleaner. The throttle 1 is realised by two 
transverse pipes 8, which penetrate the flow pipe 7 almost entirely. The 
transverse pipes 8 display a circular cross-section, as can be seen from 
FIGS. 1 and 4. 
The ratio of the diameter of the flow pipe 7 to the diameter of a 
transverse pipe 8 is approximately 2:1. 
The throttle 1 takes the form of an approximately rectangular slot 2 at its 
narrowest point, as can be seen from FIG. 3. The slot is not totally 
rectangular; rather, the slot is slightly curved and is defined by the 
curvature of the inner wall of the flow pipe. 
A displacement body 3 is arranged downstream of the slot 2 in the direction 
of flow, which is indicated by an arrow at the top edge of FIGS. 1, 2 and 
4. This displacement body 3 is of tubular design in the practical example 
shown here, i.e. essentially a hollow cylinder with a circular 
cross-section. The ratio of the diameter of the displacement body 3 to the 
diameter of the transverse pipes 8 is roughly 1:3. 
The displacement body 3 extends over the entire length of the slot and is 
arranged to be movable towards and away from the slot 2. In the practical 
example shown, the displacement body 3 can be adjusted by means of a 
spindle drive 13. The spindle drive 13 is operated manually via a 
handwheel 15. 
Two roughly parallel venturi grooves 6 are arranged between the walls 4 of 
the throttle 1 and the outer wall 5 of the displacement body. The 
cross-sections of these two venturi grooves 6 can be adjusted as desired 
by moving the displacement body 3. 
FIG. 4 shows two different enlarged and detailed settings of the 
displacement body 3 within the throttle 1. The closer to the throttle 1 
the displacement body 3 is moved, the narrower the slot widths of the two 
venturi grooves 6 become. 
The diameter of the transverse pipes 8 and the diameter of the displacement 
body 3 are matched to each other in such a way that the displacement body 
3 can completely close the throttle 1 under extreme circumstances. 
Guide plates 9 are arranged between the inner wall of the flow pipe and the 
surface areas of the transverse pipes, both upstream and downstream of the 
slot 2. 
As can be seen from FIG. 3, the displacement body 3 is positioned with its 
face ends 10 in positive contact with the adjacent inner walls of the flow 
pipe. Furthermore, recesses 11 are provided in the face ends 10 of the 
displacement body 3 and matching guide rails 12 are arranged on the 
adjacent inner walls of the flow pipe. 
Two swirl nozzles 14 for injecting the cleaning fluid are arranged above 
the throttle 1, being set in such a way that the cleaning fluid is 
injected parallel to the direction of flow. 
As can be seen from FIG. 1, the flow pipe 7 extends in roughly L-shaped 
fashion, and is provided with a flange 16 to which a centrifugal separator 
can be connected. 
LIST OF REFERENCE NUMBERS 
1 Throttle 
2 Slot 
3 Displacement body 
4 Wall 
5 Outer wall of displacement body 
6 Venturi groove 
7 Flow pipe 
8 Transverse pipe 
9 Guide plate 
10 Face end 
11 Recess 
12 Guide rail 
13 Spindle drive 
14 Swirl nozzle 
15 Handwheel 
16 Flange