FR2806416A1 - Gaseous mixture contains liquefied petroleum gas in gaseous form and additional gas selected from nitrogen, carbon dioxide, methane and ethylene, for use as high velocity oxy-combustible gas - Google Patents

Abstract

A gaseous mixture of temperature at least +15 deg C and under a pressure of at least 5 bars comprises liquefied petroleum gas (LPG) under gaseous form and at least one gaseous compound B selected from N2, CO2, H2, He, CH4, C2H4, Ar or a mixture of N2 and up to 5% of O2. Preferred Features: The mixture comprises 3-20 (especially 5-15) vol.% of gaseous compound B, and balance LPG and accidental impurities. The gaseous mixture has a temperature of 15-45 deg C, preferably 20-35 deg C and is under a pressure of 5-12 bars, preferably 7-10 bars. Independent claims are also included for the following: (i) the use of the above mixture as a combustible gas in the thermal treatment of materials or parts (preferably one part of the above mixture is mixed with burning gas or a mixture of gases), especially the thermal projection of at least one coating material (metal, alloy, WC type composite with Co matrix, ceramic or plastic material, or their mixture) onto at least one part to be coated; and (ii) the production of the above gaseous mixture, comprising vaporizing LPG by heating to at least +15 deg C at least 5 bars, and injecting at least one additional gas B as above into gaseous LPG, in such manner as to produce a homogeneous gaseous mixture.

Description

The present invention relates to a gas mixture, at a temperature of at least 5 ° C. and at a pressure greater than or equal to 5 bars, containing, on the one hand, LPG (liquefied petroleum gas) in gaseous form and, on the other hand on the other hand, at least compressible, for example nitrogen or carbon dioxide, as well as the use of such a gaseous mixture in a heat treatment operation, in particular of thermal spraying of the HVOF type.

In certain applications, in particular in HVOF (High Velocity -Fuel = high velocity oxy-fuel) thermal spraying, it is necessary to obtain minimum LPG supply pressure of at least 5 bars, sometimes at least 10 bars.

However, gasified gases are sensitive to recondensation which depends on temperature and pressure, that is to say that gasified LPGs tend to reliquefy under certain temperature and pressure conditions.

For example, for a propane gas pressure (C3H8) of the order of 7 bars at a temperature of 15 C, it has been observed that the at least partially reliquefies in the pipeline which conveys it and it then results in untimely stops of the burner located downstream of the ce pipeline, due to disturbances in the distribution of gaseous LPG therefrom, which necessitates frequent cleaning of the supply members, in particular mass flow regulator, electronic flow control member regardless of the upstream and downstream pressure, regulator ...

To avoid this problem of gaseous LPG reliquefaction, the pipes supplying the work tools, such as a burner, a torch, etc., must be equipped with a heating and / or thermal insulation device.

However, this device may prove to be insufficient for pressures greater than 7 bars, taking into account the flow rates used. When the gas pressure increases, the molecules hit the walls of the container or the pipe containing them more frequently and, in the same way, collide more frequently.

Part of their displacement energy is therefore transferred to the walls of the container or the pipe in the form of heat.

In the case of a shock between molecules, the shock energy can reach a critical value (distance between molecules close together under the effect of ambient pressure, slow speed of movement of molecules under the effect of a low temperature) which allows to form continuous chains by electrochemical bonds, thus leading to a liquid state.

For safety reasons, in particular the non-flammability of materials under normal conditions of use, the pipes are conventionally made of copper, sometimes stainless steel, carbon steel or aluminum.

All these materials are good conductors of heat (calories or frigories).

We could improve the situation by using polymer pipes or composite or metal-polymer pipes, that is to say with an inner polymer coating, in order to block or slow down the heat transfer - loss of kinetic energy molecules.

In the case of an "insulated" pipe (insulation of the external wall), the energy, that is to say the temperature, lost is compensated by the contribution of a source of electrical energy, for example heating of the pipe, but cannot fulfill its role beyond a pressure of bars because, beyond, it would be necessary to heat the pipe homogeneously at temperatures exceeding 50 C, from which it would result in possible problems of safety, in particular an increase in the internal pressure of the pipe too great (the pressure and temperature function according to the law = RT, where P = pressure, V = volume, R = side, T = temperature). On the other hand, beyond a certain temperature (45 C) impurities contained in the LPG (such as butadiene) can polymerize which leads to viscous residues which can accumulate in the low points of the pipes.

The aim of the present invention is then to solve the above problem, namely to avoid or minimize the phenomenon of reliquefaction of gaseous LPGs at pressures above 5 bar and at temperatures of at least 15 C.

The invention therefore relates to a gaseous mixture at a temperature of at least +1 and at a pressure greater than or equal to 5 bars comprising LPG in gaseous form and at least one gaseous compound chosen from the group formed by chosen from N2, C02 , H2, He, CH4, C2H4, Ar or a mixture of N2 and at most 5% of Depending on the case, the gas mixture of the invention may include one or more of the following characteristics - at a pressure between 5 bars and 12 bars, preferably between 7 bars and 10 bars.

- at a temperature between 15 and 45 C, preferably between 20 and 35 C.

- gaseous compound is carbon dioxide (C02), nitrogen (N2), methane (CH4), hydrogen (H2) and ethylene (C2H4), preferably - content of gaseous compound is 3% in flight. à in vol., preferably between 5% in vol. and 15% by volume, the remainder being gaseous LPG of any impurities.

- is a mixture of propane (C3H $) and at least one compound chosen from propylene (C3H6) and butane (C4H, o).

The invention also relates to the use of a gaseous mixture according to the invention as a combustible gas in a material heat treatment operation or of a workpiece, preferably at least part of said gaseous mixture is mixed with a gas or an oxidizing gas mixture. Preferably, the heat treatment operation is a thermal spraying operation, in particular of the HVOF type, of at least one coating material on at least one part to be coated with said coating material.

Advantageously, the coating material is a pure metal or metal alloy, a composite material of type W C in a metallic matrix type Co, a ceramic material, plastic, or a mixture of different materials.

The invention also relates to a process for manufacturing a gas mixture according to the invention, in which (a) LPG is vaporized by heating to a temperature of at least +1 and at a pressure of at least 5 bars , and (b) then injected into the LPG gas obtained in step (a) at least additional chosen from carbon dioxide (C02), nitrogen (N2), methane (CH4), hydrogen ( H2) and ethylene (C2H4), argon (Ar), helium (He), or gas mixture containing nitrogen and oxygen, the oxygen content being more than 5% by volume. and the remainder being nitrogen, so as to obtain a homogeneous gas mixture.

In other words, the solution of the present invention consists in artificially increasing the distance between two molecules of LPG pressures considered, by adding to the gaseous LPG at least one compressible gas, non-liquefiable at conventional temperatures, that is to say the order of - 40 C, to the exclusion of any gas or compound which may be oxidizing since, for obvious safety reasons, the combustible gas must not be mixed in the pipeline with an oxidizing gas. This or these additional gases may in particular be C02, N2, H2, CH4, C2H4 ...

The invention will now be described in more detail using comparative examples, given by way of illustration but not limitation.

<U> Examples </U> It can be seen that, for addition gas contents higher than 5%, LPG liquefaction phenomenon is reduced, namely for approximately 7 a of N2, the pressure of LPG in a pipeline conventionally insulated (25- wall temperature) can easily reach 10 bars without even partial liquefaction of LPG.

on the other hand, the heating power of the N2 + LPG mixture may be slightly reduced, given the presence of N2 which can absorb part of the combustion energy at the burner.

on the other hand, we note that LPG, in particular commercial propane which is a variable composition, in particular a mixture of C3H $ 1C3H6, C3H8IC4H, o mainly, with variable contents of C3H6 and C4H, o, is homogenized in terms of its performance heating.

instead of using an "inert" gas, it is also possible to use a compressed gaseous fuel.

Thus, hydrogen or ethylene make it possible to fulfill the functions described above, that is to say that contents between 5 and 10% are sufficient to delay liquefaction of the LPG beyond 7 bars of pressure.

According to the present invention, the LPG gas mixture and addition gas can be obtained or manufactured according to the following process.

is first vaporized (carbonated) either by natural evaporation, or by vaporizer (water bath, etc.) or any other suitable means, at the pressure required for the application (> _ 5 bars).

 After vaporization at the required pressure, a liquefaction retardant diluent is injected by an appropriate means, for example, by venturi type injection or injection perpendicular to the flow of LPG for better homogenization of the mixture of LPG and additional gas.

Then, the gaseous mixture is sent to the injection system pipe. It may include non-return valves, possibly a pressure and flow regulation system depending on the LPG supply pressure. The use of nitrogen as additional gas has the advantage of being able, in addition, to inert the pipe during a prolonged shutdown of the installation, thus increasing the degree of safety of the assembly, since there is no fuel stored under pressure in the pipeline and therefore no combustible gas leak.

On the other hand, the nitrogen can be reheated by an appropriate means (for example passing the nitrogen at a higher pressure than the pressure through a pre-heating regulator with a pressure variation between the inlet and the outlet of at least bars ) at a temperature between 30 C and 50 C before injection in order to limit the heating of the pipeline.

However, the use of an additional combustible gas, such as hydrogen, as diluent and retarder of liquefaction has the advantage of maintaining or even increasing the heating power of the LPG.

Claims (1)

<U> Claims </U> 1. Gas mixture at a temperature of at least +1 and at a pressure greater than or equal to 5 bars comprising LPG in gaseous form and at least one gaseous compound chosen from the group formed by chosen from N2, C02, H2, CH4 , C2H4, Ar or a mixture of N2 and at most 5% of gas mixture according to claim 1, characterized in that it is at a pressure between 5 bars and 12 bars, preferably between 7 bars and 0 bars. Gas mixture according to one of claims 1 or characterized in that it has a temperature between 15 and 45 C, preferably between and 35 C. Gas mixture according to one of claims 1 to characterized in that the compound gaseous is carbon dioxide (C02), nitrogen (N2), methane (CH4), hydrogen (H2) and ethylene (C2H4), preferably N2. Gaseous mixture according to one of claims 1 to characterized in that the content of gaseous compound is 3% by volume. at 20% by volume, preferably between 5% by volume. and 15% by vol., the remainder being gaseous and possible impurities. Gas mixture according to one of claims 1 to characterized in that the is a mixture of propane (C3H $) and at least one compound chosen from propylene (C3H6) and butane (C4Hlo). Use of a gas mixture according to one of claims 1 to 6 as a combustible gas in a heat treatment operation of a material or a part to be treated, preferably at least part of said gas mixture according to one of claims 1 to 6 is mixed with an oxidizing gas or gas mixture. 8. Use according to claim 7, in which the heat treatment operation is a thermal spraying operation, in particular of the HVOF type, of at least one coating material on at least one part to be coated with said coating material. 9. Use according to one of claims 7 or 8, in which the coating material is a pure metal or a metal alloy, a WC-type composite material in a Co-type metal matrix, a ceramic, plastic material, or a mixture of these different materials. 10. A method of manufacturing a gaseous mixture according to claim 1, in which (a) LPG is vaporized by heating to a temperature of at least +1 and at a pressure of at least 5 bars, and (b) then injected into the LPG gas obtained in step (a) at least additional chosen from carbon dioxide (C02), nitrogen (N2), methane (CH4), hydrogen (H2 ) and ethylene (C2H4), argon (Ar), helium (He), or gas mixture containing nitrogen and oxygen, the oxygen content being more than 5% in vol. and the remainder being nitrogen, so as to obtain a homogeneous gas mixture.