DE10257836A1 - Supply system for cryogenic liquefied gas with enthalpy control - Google Patents

Abstract

The control and regulating device for the enthalpy-dependent metering of a cryogenic liquefied gas or gas mixture has a heated temperature sensor (6) for controlling and regulating the metering.

Description

The invention relates to a control and control device for the enthalpy-dependent Dosage of a cryogenic liquefied Gases or gas mixture, their use and a corresponding Method.

For cooling or freezing applications such as. Cryogenic liquefied gas is found in mixers, cutters or tumblers as a refrigerant used. These applications mostly work with a clocking Injection of the liquid gas in adjustable time intervals and adjustable total time in order an overshoot avoid the temperature below the set point. The parameters are Product-related determined in preliminary tests.

• – Bei längeren Versorgungsleitungen ist zur Erzeugung einer gleichmäßigen Kälte ein druckgesteuerter Gasphasenabscheider erforderlich.
• – Das Taktzeitverfahren berücksichtigt nicht die thermische Vorgeschichte der Anlage.
• – Das Kaltfahren einer warmen Anlage dauert wegen der konstanten Einspritzpausen länger als erforderlich.
• – Das Taktzeitverfahren berücksichtigt nicht den tatsächlichen Kälteinhalt des Flüssiggases, der vom Zustand (Druck, Temperatur, Phase) des Flüssiggases abhängt. Die Endtemperatur eines bestimmten Produktes ist daher durchaus unterschiedlich.

The known devices have the following disadvantages:

• - In the case of longer supply lines, a pressure-controlled gas phase separator is required to generate even cooling.
• - The cycle time method does not take into account the thermal history of the system.
• - The cold running of a warm system takes longer than necessary due to the constant injection pauses.
• - The cycle time method does not take into account the actual cold content of the liquid gas, which depends on the state (pressure, temperature, phase) of the liquid gas. The final temperature of a certain product is therefore quite different.

The object of the invention is a alternative dosing of a cryogenic liquefied gas or gas mixture ready to provide.

The task is solved by a control and regulating device with those described in claim 1 Features.

The control and regulating device for the enthalpy-dependent metering of a cryogenic liquefied gas or gas mixture has a heated temperature sensor ( 6 ) on.

Cryogenic liquefied gases (liquefied gases) are more fluid, for example Nitrogen, liquid Air, liquid Carbon dioxide, liquid Argon, more liquid Hydrogen or liquid Helium.

For the final temperature of a product to be cooled is at constant initial conditions on the product side and firmer cooling time the cooling capacity of the liquid gas (cryogenic liquefied Gas or gas mixture) decisive. The cooling capacity is dependent on the enthalpy and the mass flow of the liquid gas.

The cooling capacity of the liquid gas, or an indirect size, here the measured value of the heated temperature sensor in front of the injection valve (metering valve) is detected and with the Setpoint compared. In the event of deviations, the pulse / pause ratio of the Injector adjusted. In the case of a negative system deviation the pulse duration is extended at the expense of the break and in the event of a positive control deviation shortened, so about that Time a constant cooling energy to disposal is provided. With constant, product-related starting conditions are the desired ones Final product temperatures reached; the thermal history the feeding devices (Pipeline, injection valve) is taken into account.

The invention is based on the drawing explained.

1 shows a liquid gas supply system with an insulated storage container ( 1 ) for the refrigerant, e.g. liquid nitrogen, a sampling valve ( 2 ), a safety valve ( 3 ), a control or regulating device ( 4 ), an electric heater ( 5 ), a temperature sensor ( 6 ), an injection valve or dosing valve ( 7 ) and a consumer ( 9 ) for the refrigerant, e.g. a mixer, tumbler or cutter.

The temperature sensor ( 6 ) of the control or regulating device ( 4 ) is located with the electric heater ( 5 ) in a common protective tube made of thin-walled material, e.g. stainless steel. The protective tube is installed in the feed line to the injection valve so that the refrigerant flows around it. The temperature sensor ( 6 ) can preferably be a Pt-100, but also a thermocouple, an electrical carbon film resistor or a semiconductor. The heating power of the electric heater ( 5 ) is so small that when using a double Pt-100, the second Pt-100 with an additional series resistor can serve as a heating circuit. As a control device ( 4 ) a temperature controller can be used.

The injector ( 7 ) can preferably be a solenoid valve, a pneumatically controlled open-close valve or a control valve ( 8th ) his.

function

1st cycle operation with solenoid valve / pneumatically controlled on-off valve

After the start of the cooling process, the first cycle starts with the opening of the injection valve ( 7 ). The heated temperature sensor ( 6 ) is cooled by the mass flow of the liquid gas depending on its enthalpy. The control device ( 4 ) works with constant but adjustable cycle times, in which the pulse and pause duration is changed depending on the control deviation. The pulse duration can vary in the range of, for example, 20% to 80% of the cycle time, depending on the control deviation. After the pulse and the pause time has elapsed, a new cycle begins. As soon as the temperature setpoint is reached, the injector ( 7 ) closed and only opened again when exceeded in the next cycle.

2. Continuous operation with control valve

After the cooling process has started, the control valve ( 8th ). The heated temperature sensor ( 6 ) is cooled by the mass flow of the liquid gas depending on its enthalpy. The cross section of the control valve is corrected depending on the control deviation.

Claims (8)

Control and regulating device for the enthalpy-dependent metering of a cryogenic liquefied gas or gas mixture, which a heated temperature sensor ( 6 ) having. Control and regulating device according to claim 1, characterized in that the control and regulating device is a controllable valve ( 7 ) for dosing the cryogenic liquefied gas or gas mixture. Control and regulating device according to claim 1 or 2, characterized in that the temperature sensor ( 6 ) with a control or regulating unit ( 4 ) connected is. Control and regulating device according to one of claims 1 to 3, characterized in that the temperature sensor ( 6 ) and a controllable valve ( 7 ) on a line leading the cryogenic liquefied gases or gas mixture to a consumer ( 9 ) leads, are arranged. Method for operating a supply system for a cryogenic liquefied gas or gas mixture, in which a consumer ( 9 ) The amount of cryogenic liquefied gas or gas mixture supplied is controlled or regulated depending on the mass flow of the cryogenic liquefied gas or gas mixture. A method according to claim 5, characterized in that more fluid Nitrogen liquefied as cryogenic Serves gas. Use of a control and regulating device after one of the claims 1 to 4 in a supply system for a cryogenic liquefied Gas or gas mixture. Use according to claim 7, characterized in that that the supply system with a mixer, tumbler or cutter connected is.