DE102005053341A1 - Use of diaphragm valves for flow control - Google Patents

Abstract

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.

Description

The 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 continuous control of a gas or liquid flow.

In Many chemical manufacturing processes are for an accurate process analytical Measurement of the measurement and control of a flow rate of a gas involved in the chemical reaction, a liquid, as the reactants but also the reaction mixture necessary. Often it acts it is also highly toxic gases or liquids such. Phosgene, so that the control units in addition to a precise volume control on a extraordinary Tightness have to.

In Usually flowmeters are equipped with an initiator are used. This initiator works as a binary contact and gives information about whether the flow over 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 controls then over a converter a servomotor to a needle valve. alternative there are analog systems that over have a bypass capillary, but hardly because of the strong constipation tendency of the capillary is used.

These However, orders have not the crucial disadvantage over one for highly toxic Media sufficient tightness to dispose. Basically, for handling highly toxic media the greatest possible tightness required.

since For many years, pneumatically actuated, metal-sealed diaphragm valves as "open / close" high-tightness valves In the industry in use and proven, such as valves DP series from Swagelok Company, Ohio or Parker so model VSM TYPE 944 AOP LP.

These Valves become conventional However, only used in on / off circuit, as according to prevailing Opinion these systems only discreetly and not continuously driven can be.

It was now surprising found that one is the commercial one Diaphragm valves very well also continuously drive and thus in principle, regulate a flow as desired or keep it constant can. For this purpose, the flow according to the invention by a commercial analog flow meter, z. measured the DK37 of the company Krohne, and over a PID controller a current-pressure converter is driven, in turn a commercial one pneumatically controlled diaphragm valve, which a corresponding to be controlled line path sits steplessly steers and so the flow steplessly regulates.

Amazingly, One can by the appropriate use of these diaphragm valves the flows just as precise as with needle valves.

One The first subject of the present application is therefore the use of diaphragm valves for stepless control of a fluid flow rate.

One Another object of the present application is a device for continuous control of a fluid mass flow, containing a diaphragm valve.

One Another object of the present application is a system for Production of any product, characterized in that at least a fluid flow rate by means of a device containing a Diaphragm valve is controlled.

Of the inventive structure and the use according to the invention are basically for all Suitable method in which monitored gaseous or liquid streams and are controlled, especially for processes in which material flows high toxic substances, e.g. Phosgene, need to be controlled.

Examples for 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 ( 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 Regulation is as follows constructed: The measured product flow becomes analogous to the PID controller Form fed as actual value. The controller provides depending on from the setpoint / actual value comparison, an analog signal that is an I / P converter supplied becomes. This I / P converter shapes the current signal into a pneumatic one Signal to, which is then applied to the diaphragm valve. On In this way, the flow can be regulated very accurately.

Of course you can too other arrangements and components are chosen which determine the flow, the derivation of a control signal and finally the ensure 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 membrane 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 to be contrary to the prevailing flow Steer infinitely regulate opinion by means of a diaphragm valve.

Claims (6)

Use of diaphragm valves for stepless Control of a fluid flow rate. Device for stepless control of a fluid Flow rate, containing a diaphragm valve. Process for the preparation of a product, characterized characterized in that at least one fluid flow rate using a diaphragm valve is steplessly controlled. Method according to claim 3, characterized in that the product bisphenol A (BPA), diphenyl carbonate (DPC), polycarbonate (PC), methylenediphenyl diisocyanate (MDI), tolylene diisocyanate (TDI), Hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI). Plant for producing a product characterized that at least one fluid flow rate by means of a device is controlled according to claim 2. Plant according to claim 5, characterized in that the product bisphenol A (BPA), diphenyl carbonate (DPC), polycarbonate (PC), methylenediphenyl diisocyanate (MDI), tolylene diisocyanate (TDI), Hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI).