EP0000187B1 - Method for the reduction of noise during the throttling of vapour and gas flow - Google Patents

Description

The invention relates to a method for noise reduction in the throttling of steam and gas flows, in which the divided flows are relaxed in a supercritical manner over a short flow section.

The relaxation of gases or vapors is necessary for the control in process engineering plants. Such a process step often occurs particularly in chemical processes. This creates unwanted noises that lead to harassment at the workplace and disturb the surroundings.

It is known to split a stream into partial streams, which are individually expanded in one step to the desired pressure.

With this method, noise level reductions of up to 15 dB (A) can be achieved, which are generally not sufficient. The reason for the low noise level reduction is given by the geometric dimensions. On the one hand, the holes for the partial flows cannot be made arbitrarily small, since then the operational safety is endangered by contamination. On the other hand, the sizes become bulky with large quantities. It has also been found that a one-step pressure reduction in no way leads to optimal sound level reductions.

Furthermore, throttling can be realized by step resistors connected in series.

The effectiveness of the noise level reduction depends crucially on the step pressure gradient, which is determined by the design of the step resistors. An adjustment to certain operating conditions is therefore hardly possible afterwards. Manufacturing errors also have an unfavorable effect. Furthermore, such constructions are often very complex, so that they require a lot of maintenance in addition to high investment costs.

A method has to be found which allows the low-noise expansion of gases and vapors with simple, maintenance-friendly and reliable measures which can be adapted to the required procedural and acoustic conditions without difficulty.

This object is achieved in that after their relaxation in the first flow section, the flows are then divided and slowed down in a directly subsequent second flow section, the flow cross-sections in the second flow section being individually smaller than in the first flow section but being essential as a whole are larger than the totality of the flow cross sections in the first flow section.

It was surprising for a person skilled in the art that a level reduction of 30 dB (A) is possible with this method. This is due to the fact that the potential energy of the flow is converted into kinetic energy in accordance with the pressure ratio in the first segment after being divided into partial flows, and in the second segment the kinetic energy is converted into heat by friction. It is important that the energy conversion is intensified and low-noise in the second section due to the relatively narrow outflow spaces. In addition, the narrow flow cross-sections result in an increase in frequency of the maximum of the radiated sound spectrum. The second route is not intended to reduce potential energy. This method also gives good control characteristics.

After a special implementation of the method, the flow cross section in the second section is expanded by 1.5-15 times the product of the quotient inlet pressure to final pressure times the flow cross section of the first section.

Through this expansion of the cross-section, the free jets are discharged in such a way that unification of the free jets and thus additional sound generation is avoided.

In a further implementation of the method, the characteristic distances between the boundary walls of the river cross sections in the second section are smaller than the mean wavelength of the emitted sound spectrum. By adhering to this condition-wavelength to the characteristic distance, which among other things is also included in the Strouhal number - it is achieved that the impedance jumps thus achieved lead to sound insulation.

When the method is carried out further, the relaxation in the first section is divided into several stages, which has proven to be advantageous particularly in the case of extremely high pressure drops.

Claims (4)

1. Process for reducing noise during the throttling of streams of vapour or gas, in which the divided streams are let down in the supercritical state in a short section of flow, characterised in that, in a second section of flow immediately downstream of the first, the streams are then divided into several streams and slowed down, the flow cross-sections in the second section of flow individually being smaller than in the first section of flow, but their total being substantially greater than the total of the. flow cross-sections in the first section of flow.

2. Process according to Claim 1, characterised in that the total flow cross-section in the second section of flow is increased by 1.5-15 times the product of the quotient of initial pressure to final pressure and the total flow cross-section of the first section of flow.

3. Process according to Claims 1 to 2, characterised in that the characteristic distances between the limiting walls of the flow cross-sections in the second zone are smaller than the average wavelength of the sound spectrum radiated.

4. Process according to Claims 1 to 3, characterised in that the letting-down in the first section of flow is a multi-stage operation.