Refrigeration – Storage of solidified or liquified gas
Patent
1996-12-31
1998-05-19
Capossela, Ronald C.
Refrigeration
Storage of solidified or liquified gas
62614, 62616, F17C 100
Patent
active
057523860
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of draining a tank containing a vapourized gas--after draining of its contents of liquified gas--by supplying to the tank vapourized nitrogen which is stored in liquid state in a supply. Moreover, the invention relates to a plant for use in draining of such a tank, comprising a supply of liquid nitrogen to be supplied to the tank in vapourized state.
Nitrogen is supplied in order to remove residues of combustible gases in tanks, and also in order to prevent the tanks in containing a mixture of different gases when one type of gas is to replace another type. Vapourized nitrogen, thus, is supplied to the tanks after substantially draining their contents of liquid gas, in order to expel the residues of the vapourized gases present in the tanks. The residual gases may be burnt or discharged into the atmosphere. Thereby a contamination takes place, because of the combustion or because the gases as such are contaminating. Moreover, a not insignificant amount of residual gas is lost each time this is carried out, which has been accepted as unavoidable.
Another aspect of flushing tanks with nitrogen is that the nitrogen is stored in liquid state, resulting in consumption of heat for vapourization of the nitrogen prior to supplying it to the tanks. The surrounding air may indeed be used as a heat emitting medium for the vapourization, but thereby the large cooling capacity of the liquid nitrogen is not utilized for anything else than cooling the air which causes the vapourization.
According to the present invention a method and a plant have been provided which at the same time permit recovery of the contents of residual gases in vapourized state in tanks whose contents of liquid gas have been drained and vapourization of liquid nitrogen to be supplied to the tanks by utilization of the heat in the residual gases.
The method and plant according to the invention appear from the succeeding claims.
According to the invention residual gases in vapourized state are expelled from an incompletely drained tank, in order to undergo heat exchange with liquid nitrogen to be supplied to the tank. The heat of the vapourized residual gases is utilized for vapourization of the nitrogen, and the residual gases can be condensed into liquid state in order to be recovered.
The invention may be utilized in landbased as well as in floating plants, for tanks on vehicles (trucks, railway), gas carrier ships, stationary onshore and offshore plants. In all cases is achieved that discharge of residual gases to the atmosphere or the development of combustion gases by combustion of the residual gases is avoided.
For all of the most common gases transported in liquid state the boiling point is substantially higher than that of nitrogen, whose boiling point is -197.degree. C. (at atmospheric pressure), and when the residual gases are at their boiling point a large temperature difference will occur during the exchange of heat. The residual contents in a tank after incomplete drainage may for instance have the following temperature, depending on the type of gas: ethylene -100.degree. C., ethane -80.degree. C., propylene -45.degree./-20.degree. C., propane -40.degree./-20.degree. C., NH.sub.3 -33.degree. C., butadiene and butylene +1.degree. C., butane -3.degree. C., i.e. slightly higher than the boiling point at atmospheric pressure. The residual contents of such gases in a tank after a usual (incomplete) drainage may be estimated as follows, when the volume of the tank is 6500 m.sup.3 : ethylene 17000 kg, ethane 19500 kg, propylene 17000/42500 kg, propane 17000/35500 kg, NH.sub.3 5700 kg, butadiene 18500 kg, butylene 20800 kg and butane 19500 kg.
The plant may of course have several recovery tanks, at least one for each type of residual gas to be collected.
The heat exchange may take place in two steps. Residual gas supplied from the tank which is incompletely drained can be conveyed to a first heat exchanger or a group of heat exchangers, in which exchange of heat takes place between vapourized, cold nit
REFERENCES:
patent: 3214927 (1965-11-01), Bengtsson
patent: 3216211 (1965-11-01), Pauliukonis
patent: 3699696 (1972-10-01), Rhoton
patent: 3965689 (1976-06-01), Brown et al.
patent: 5005362 (1991-04-01), Weltmer, Jr. et al.
patent: 5367881 (1994-11-01), Henzler
Brendeng Einar
Jonas J.o slashed.rn M.
Norberg B.ang.rd
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