This application is based upon and claims the benefit of the priority of Japanese patent application No. 2007-131670, filed on May 17, 2007, the disclosure of which is incorporated herein in its entirety by reference thereto.
This invention relates to a liquefied gas supply system and method by controlling heating of a plurality of liquefied gas containers.
When a large volume of liquefied gas whose vapor pressure is low and therefore vaporization volume is low at an ordinary temperature is necessary, methods to increase vaporization surface area or to raise the gas temperature are used. And increasing a diameter of a container of the gas, parallel connection of containers having a standard volume or heating the container is effective to realize the methods. Therefore, a system has been developed to supply huge volume of the gas constantly by the parallel connection of the containers having a standard volume which is easily available, heating the gas container or combination of them.
JP Patent Kokai Publication No. JP-H11-226386A
JP Patent Kokai Publication No. JP-2003-28395A
JP Patent Kokai Publication No. JP-2006-161937A
The entire disclosures of Patent Documents 1 to 3 are incorporated herein by reference thereto. The following analyses are given by the present invention.
The controlling method of liquefied gas supply system described in
The supply system and method of liquefied gas shown in
The conventional liquefied gas supplying method shown in
The liquefied gas supplying system having a plurality of gas cylinders as shown in
According to the inventor's findings, the liquefied gas is transported between containers by a very small difference of the temperatures such as an influence of a flow of the air in a room where the containers are placed, for example. Therefore, a control of heating using the temperature of the liquefied gas itself is necessary to prevent the transportation of the gas; however, it is difficult to measure the temperature of the liquefied gas itself.
As explained above, there are two problems in the conventional systems or methods. One of them is the unbalanced consumption of the liquefied gas when supplied, that is, when a plurality of liquefied gas containers are used in parallel, only the gas in the container whose vapor pressure is higher is consumed due to a temperature difference between containers irrespective of the provision of the heating means. The other problem is the transportation of the liquefied gas between containers, that is, when the gas supply is stopped, the liquefied gas is transported from a container whose vapor pressure is higher to a container whose vapor pressure is lower through connection piping.
It is an object of the present invention to provide a supply system and supply method of liquefied gas which can supply the liquefied gas stored in a plurality of liquefied gas containers uniformly up to a final stage in order to supply a huge amount of gas stably.
According to the present invention, the problem is solved by controlling each heating device based on a value obtained by an overall processing of the information obtained from all (each of) the containers at every instance, without recourse to the controlling based on a predetermined value.
According to a first aspect of the present invention, there is provided a liquefied gas supply system comprising: a plurality of liquefied gas containers, a detector installed in each of the containers that detects a volume of liquefied gas contained in each of the container, a heating device installed on each of the container, and a control device that processes information obtained by each of the detectors and controls each of the heating devices. The control device controls each of the heating device based on a value obtained by a comprehensive (i.e., overall) processing of the information obtained by all of the detectors.
A measurement item can be a weight or a volume (bulk) of the liquefied gas in the container. Also a liquid level of the liquefied gas may be used. Any known measurement method can be used for the measurement.
As a second aspect of the liquefied gas supply system of the present invention, each detector is a weight detector of the liquefied gas.
As a third aspect of the liquefied gas supply system of the present invention, the value is an average weight obtained by averaging all weights of the liquefied gas in the containers, and the control device controls each of the heating devices so that a difference between a weight obtained by a detector of a container concerned and an average weight becomes smaller than a predetermined value.
As a fourth aspect of the liquefied gas supply system of the present invention, each of the detectors is a level detector of the liquefied gas.
As a fifth aspect of the liquefied gas supply system of the present invention, the value is an average level obtained by averaging all levels of the liquefied gas in the containers, and the control device controls each of the heating devices so that a difference between a level obtained by a detector of a container concerned and the average level becomes smaller than a predetermined value.
According to a sixth aspect of the present invention, the liquefied gas supply system comprises a connection shut off valve to shut off connection lines between the containers coupled with a closing valve to shut off supply of the gas.
According to a seventh aspect of the present invention there is provided a liquefied gas supply method to supply the gas from a plurality of liquefied gas containers. The method comprises: controlling each heating device installed on each of the liquefied gas containers using a processed information obtained from each detector installed on each of the liquefied gas containers to detect a volume of the liquefied gas in each of the liquefied gas containers. Each of the heating devices is controlled based on a value obtained by a comprehensive (i.e., overall) processing of information obtained from all of the detectors.
As an eighth aspect of the liquefied gas supply method of the present invention, each of the detectors is one of a weight detector and a level detector of the liquefied gas.
According to a ninth aspect of the present invention, there is provided a control device of a liquefied gas supply system to control each heating device installed on each liquefied gas container. The control device uses a processed information obtained from each detector installed on each of the liquefied gas containers to detect a volume of the liquefied gas in each of the liquefied gas containers. Each of the heating devices is controlled based on a value obtained by a comprehensive (i.e., overall) processing of information obtained from all of the detectors.
In a tenth aspect of the present invention, each of the detectors may be one of a weight detector and a level detector of the liquefied gas.
The meritorious effects of the present invention are summarized as follows. The liquefied gas in a plurality of liquefied gas containers is consumed uniformly by using the present invention. That is, a necessary vaporization capacity at a predetermined temperature can be maintained from the beginning of supply of the liquefied gas up to the end because all of the gas in the containers are consumed uniformly and a necessary vaporization surface area is maintained constant by keeping connections between all of the containers.
In the accompanying drawings:
A liquefied gas supply system and a temperature control method of the present invention are described using some exemplary embodiments in detail with reference to the figures.
Each of the containers 1-1 to 1-n has the same size and capacity and each of the liquefied gas volume 10-1 to 10-n (in weight for this example 1) is known before setting in the system. All of the containers are connected each other by the connection piping 8 in parallel and collected toward the shut off valve 9.
Under this state, the volume (in weight for this example) in each of the containers is measured by the weight detectors 2-1 to 2-n continuously and the measured values are transmitted to the processor/comparator of measured values 7. And the heaters 3-1 to 3-n and the heat sensors 4-1 to 4-n are installed on containers 1-1 to 1-n, respectively. The required temperature computed by a known relation between temperature and vapor pressure of the liquefied gas is set in the temperature controllers 5-1 to 5-n and the processor/comparator of measured values 7 controls the temperature of the liquefied gas 10-1 to 10-n by the heaters 3-1 to 3-n via the heat output units 6-1 to 6-n by PID control. The processor/comparator of measured values 7 calculates the transmitted measured values, compares the measured value with the calculated value and outputs a stop signal when the result satisfied a condition. Thus the processor/comparator 7 compensates an output of the heat output units 6-1 to 6-n by interrupting heating control outputs outputted from the temperature controllers 5-1 to 5-n.
In
Also in
According to a conventional method, every container is controlled merely by the temperature controllers 5-1 to 5-n to keep the temperature measured by the heat sensors 4-1 to 4-n at a determined value. In other words, the control is done one by one (i.e., individually independently from one to another wherein actual liquefied gas temperatures in the containers become slightly different from one another. Therefore, the gas vaporized from a container of higher temperature is re-condensed in a container of lower temperature (liquefied gas transportation) or the gas in a container of higher temperature is consumed faster (imbalanced consumption) when the gas is supplied.
In contrast, according to example 1 of the present invention, the weights of the liquefied gas remaining in the containers are measured (monitored) by the weight detectors 2-1 to 2-n at all times, and when the remaining liquefied gas volume (weight) becomes smaller than some value which is obtained by processing all of the measured values totally (mean value in example 1) by a predetermined value D or more, the heating of the container is forcively stopped and the evaporation of the liquefied gas is suppressed. The process is repeated at regular intervals and the heating is stopped during the interval for measuring/comparing as necessary.
In the case of
As described above, the remaining liquefied gas volume in each container is compared with the average value and heating of containers whose consumptions are larger than average are stopped forcively by compulsion. Thus all of the liquefied gas 10-1 to 10-n in the containers 1-1 to 1-n decrease uniformly without imbalanced consumption to the end. Therefore, a necessary vaporization capacity at a predetermined temperature can be maintained from the beginning of a supply of the liquefied gas to the end because all of the gas is consumed uniformly and a necessary vaporization surface area is decreased under uniformly maintaining the required vaporization surface area by keeping connections between all of the containers.
The capacity of each container is assumed to be the same in example 1; however, it is not necessary. However, the average value of the remaining gas volume (weight) cannot be used as a standard value. In such a case, a ratio of the remaining gas volume in the container concerned to the whole capacity of the container is calculated for each container and an average value of the ratios can be used as a standard value, for example.
Cubic contents (volume) can be used as a volume of the liquefied gas instead of weights. The present invention can be carried out by substituting cubic contents for weights in example 1.
Example 2 will be explained with reference to
The remaining volume of the liquefied gas is detected by the liquid level sensor directly in example 2. The direct measurement of the liquid level has less interference than detecting the weight of the containers, that is, piping connected to the container influences the detection of the weight as example 1, for example. The liquid level measurement has an additional advantage that when remaining weight of the gas differs from each other due to a shape or a cross sectional area of the container, it is possible to control the decreasing liquid levels uniformly.
Example 3 will be explained using
In this situation, the liquefied gas in a container of a higher gas pressure moves to another container of a lower gas pressure due to a small difference in the gas pressure generated by a temperature difference between the two containers (liquefied gas transportation). And the gas volumes in the containers are balanced by the control system of the present invention even in the standby state; however, it is not necessary to balance the volumes in the containers using the control system especially when the closing valve 9 is shut off and the gas is not supplied. Therefore, the connection braking valves 12-1 to 12-n may be closed to shut off connections between the containers temporarily in relation to the closing valve 9. During the connection-braking state, the stop signal outputs OFF-1 to OFF-n are not outputted and the containers are controlled by only the temperature controllers 5-1 to 5-n.
If the processor/comparator 7 failed and the stop signal output was not outputted or the heaters 3-1 to 3-n became out of order when the liquefied gas supply system is under standby state with a full volume of the gas, there is a risk that the liquefied gas may overflow from a container of lower temperature by the transportation of the liquefied gas due to the temperature difference between containers. The system shown in example 3 can eliminate this risk by shutting off the connections between containers by closing the connection braking valves 12-1 to 12-n.
It should be noted that other objects, features and aspects of the present invention will become apparent in the entire disclosure and that modifications may be done without departing the gist and scope of the present invention as disclosed herein and claimed as appended herewith. Also it should be noted that any combination of the disclosed and/or claimed elements, matters and/or items may fall under the modification aforementioned.
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Number | Date | Country |
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11-226386 | Aug 1999 | JP |
2003-028395 | Jan 2003 | JP |
2006-161937 | Jun 2006 | JP |
Number | Date | Country | |
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20080282709 A1 | Nov 2008 | US |