WO2007051559A1

WO2007051559A1 - Use of diaphragm valves for flow regulation

Info

Publication number: WO2007051559A1
Application number: PCT/EP2006/010314
Authority: WO
Inventors: Christoph Schwinning; Wolfgang Brachmann
Original assignee: Bayer Technology Services Gmbh
Priority date: 2005-11-07
Filing date: 2006-10-26
Publication date: 2007-05-10
Also published as: DE102005053341A1

Abstract

The present invention relates to the use of commercially available diaphragm valves as regulating valves for flow control, and to control devices which comprise diaphragm valves of this type for the continuous control of a gas or liquid flow.

Description

Use of diaphragm valves for flow control.

The present invention relates to the use of commercially available diaphragm valves as control valves for flow control, and control devices containing such diaphragm valves for the continuous control of a gas or liquid flow.

In many chemical manufacturing processes, the measurement and regulation of a flow rate of a gas involved in the chemical reaction, of a liquid, such as the educts but also of the reaction mixture, is necessary for an accurate process-analytical measurement. Often these are also highly toxic gases or liquids such. As phosgene, so that the control units in addition to a precise volume control must also have an extraordinary tightness.

As a rule, flowmeters provided with an initiator are used for this purpose. This initiator works as a binary contact and tells you if the flow is above or below a certain value.

A second version of this flow monitoring has two binary contacts. This version uses a special controller as input signal. This then controls a servomotor via a converter to a needle valve. Alternatively, there are analog systems that have a bypass capillary, but which is hardly used because of the strong tendency of the capillary to block.

However, these arrangements do not have the decisive disadvantage of not having sufficient tightness for highly toxic media. Basically, the greatest possible tightness is required for the handling of highly toxic media.

Pneumatically actuated, metal-sealed diaphragm valves have been used and proven in the industry for many years as "open / close" high density valves in the industry, such as the Swagelok Company, Ohio DP Series DP valves or the Parker Model VSM TYP 944 AOP LP ,

However, these valves are conventionally used only in open / close circuit since, in the prevailing opinion, these systems can only be controlled discreetly and not continuously.

Surprisingly, it has now been found that the commercially available diaphragm valves can very well also be activated continuously and thus in principle be able to regulate a flow as desired or to maintain it constant. For this purpose, the flow through a commercially available analog flow meter, z. the DK37 from Krohne and a PID controller Current-pressure converter driven, in turn, a commercially available pneumatically controlled diaphragm valve, which sits a correspondingly regulated line path, steplessly controls and so infinitely controls the flow rate.

Astonishingly, through the appropriate use of these diaphragm valves, the flows can be regulated just as precisely as with needle valves.

A first subject of the present application is therefore the use of diaphragm valves for continuous control of a fluid flow rate.

Another object of the present application is a device for continuous control of a fluid flow rate, comprising a diaphragm valve.

Another object of the present application is a plant for the production of any product, characterized in that at least one fluid flow rate by means of a device containing a diaphragm valve is controlled.

The construction according to the invention and the use according to the invention are in principle suitable for all processes in which gaseous or liquid streams are monitored and controlled, especially for processes in which streams of highly toxic substances, e.g. Phosgene, need to be controlled.

Examples of such processes are in particular processes for the preparation of bisphenol A (BPA), diphenyl carbonate (DPC), polycarbonate (PC), methylene diphenyl diisocyanate (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI).

In a preferred embodiment of the invention, the structure (sketch) of the flow control is as follows (Figure 1): In the flow direction of the substance to be controlled first sits the pneumatically controllable diaphragm valve used as an actuator. This is followed by a flow meter with analog signal output. The measured product stream is then fed to the analyzer.

The control is structured as follows: The measured product flow is fed to the PID controller in analog form as an actual value. Depending on the setpoint / actual value comparison, the controller supplies an analog signal which is fed to an I / P converter. This I / P converter converts the current signal into a pneumatic signal, which is then applied to the diaphragm valve. In this way, the flow can be controlled very accurately. Of course, other arrangements and components can be chosen, which ensure the determination of the flow, the derivation of a control signal and finally the appropriate control of the valve.

The following example is intended to illustrate the invention without, however, limiting it:

In a plant for the production of methylene diisocyanate (MDI), the phosgene concentration was measured in two monochlorobenzene streams by cyclically switching the currents to a measuring device. Since different pressures were present in the streams, the flow had to be regulated. To control this, a diaphragm valve from Swagelok Type 6LVV DPS6m-C was integrated into the system and controlled by a PID controller of a Siemens C7 and an IP converter Type 6112 from Samson. The analog signal from the flowmeter was recorded on a recorder.

It was found that the flow could be infinitely regulated by means of a diaphragm valve, contrary to the prevailing opinion.

Claims

claims;

1. Use of diaphragm valves for stepless control of a fluid flow rate.

2. A device for stepless control of a fluid flow rate, comprising a diaphragm valve.

3. A process for the preparation of a product, characterized in that at least one fluid flow rate is controlled continuously using a diaphragm valve.

4. The method according to claim 3, characterized in that the product bisphenol-A (BPA), diphenyl carbonate (DPC), polycarbonate (PC), methylene diphenyl diisocyanate (MDI), tolylene diisocyanate (TDI), hexamethylene diisocyanate (HDI) or isophorone diisocyanate

(EPDI).

5. Plant for the production of a product characterized in that at least one fluid flow rate is controlled by means of a device according to claim 2.

6. Plant according to claim 5, characterized in that the product is bisphenol A (BPA), diphenyl carbonate (DPC), polycarbonate (PC), methylene diphenyl diisocyanate (MDI), tolylene diisocyanate (TDI), hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI) ,