CA1139099A - Recovering heat from burning elemental phosphorus - Google Patents
Recovering heat from burning elemental phosphorusInfo
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- CA1139099A CA1139099A CA000375026A CA375026A CA1139099A CA 1139099 A CA1139099 A CA 1139099A CA 000375026 A CA000375026 A CA 000375026A CA 375026 A CA375026 A CA 375026A CA 1139099 A CA1139099 A CA 1139099A
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Abstract
RECOVERING HEAT FROM
BURNING ELEMENTAL PHOSPHORUS
ABSTRACT
Large quantities of valuable heat can be recovered from burning elemental phosphorus by bringing together in a reaction zone elemental phos-phorus and a sufficient amount of oxygen in a free-oxygen containing gas to form phosphorus pentoxide in a product stream while maintaining the mole ratio of water to phosphorus pentoxide to less than 1:1 in the product stream. The product stream from the reaction zone is cooled to a temperature not less than the dew point of any component in the product stream, prefer-ably to a temperature not less than about 100°C. above the dew point of any component in the product stream, by contacting the product with a metal cooling surface containing a heat transfer fluid to maintain the temperature of the metal cooling surface at least about 100°C. Heat can be recovered from the heat transfer fluid for other uses. In the preferred embodiment pressurized water is used as the heat transfer fluid to maintain the temperature of the cooling surface at about 200°C.
BURNING ELEMENTAL PHOSPHORUS
ABSTRACT
Large quantities of valuable heat can be recovered from burning elemental phosphorus by bringing together in a reaction zone elemental phos-phorus and a sufficient amount of oxygen in a free-oxygen containing gas to form phosphorus pentoxide in a product stream while maintaining the mole ratio of water to phosphorus pentoxide to less than 1:1 in the product stream. The product stream from the reaction zone is cooled to a temperature not less than the dew point of any component in the product stream, prefer-ably to a temperature not less than about 100°C. above the dew point of any component in the product stream, by contacting the product with a metal cooling surface containing a heat transfer fluid to maintain the temperature of the metal cooling surface at least about 100°C. Heat can be recovered from the heat transfer fluid for other uses. In the preferred embodiment pressurized water is used as the heat transfer fluid to maintain the temperature of the cooling surface at about 200°C.
Description
~L~.3~ k'~
3_4575 RECOVERING HEAT FROM
BURNING ELEMENTAL PHOSPHORUS
~ BACKGROUND OF THE INVENTION
This inventlon relates to a process for 5 recoverin~ valuable ener~y ~rom burning of phosphorus.
Phosphorus pentoxide is an important chemical intermediate used to prepare phosphoric acid and many other phosphorus-containing compounds. Indeed, millions of kilograms of phosphorus pentoxide are produced each year to prepare phosphoric acid for a wide variety of applications.
As is known to those skilled in the art, phosphorus pentoxide is prepared commercially by burning elemental phosphorus in a stream of dried air.
Adequate time is allowed to complete the reaction to prevent the ~ormation of lower oxldes of phosphorus.
The resulting phosphorus pentoxide can be made so free o~ lower oxides that it will not decolorize dilute permanganate solutions. The usual plant for manu-~acturing phosphorus pento~ide consists o~ a phosphorusfeed systemg provisions for drying the air, a burning chamber, and a mechanism to collect the phosphorus pentoxide. On the other hand, when phosphoric acid is the only desired end product, the air is not usually dried, and the phosphorus pentoxide is contacted with water to form the phosphoric acid.
The oxidation o~ elemental phosphorus with oxygen evolves about 5.8 million calories per kilo-gram of phosphorus. The temperatures of the gases ~rom the oxidation vary ~rom about 90oC. up to about 3,000C., dependin~ on the amount of excess gases used in the process.
Despite the presence of so much available heat from the process, this heat has not heretofore been recovered and used efficiently. The only known commercial uses of waste heat from phosphorus combus-tion are for preheating combustion air for another process by heat transfer through a re~ractory protected - wall, or for evaporation of water from soda ash solu-tions by using the solutions in the hydrator/absorber and mist collection circuits in the acid process.
The prior art on production of phosphoric acid ~rom elemental phosphorus abounds with references to the disastrous corrosive attack of the acid on metals at temperatures well below those necessary for generation of steam at useful distribution pressures. ~he condensation of polymeric acids on hot metal surfaces was thought to be particularly corrosive. The polymeric acids were commonly called '7meta acid", a term used loosely to describe any polymeric acid composition that is not fluid at room temperature. Such compositions are those above about 85 percent P205. To avoid this corrosive attack, metal surfaces were either protected by a layer of refractory material, or maintained below 100C. where the corrosion rate is tolerable on stainless steels commonly used in phosphoric acid plants. Neither of these methods are attractive for recovery of heat at useful steam distribution pressures.
It has been speculated without proof for years that heat could be recovered from the phos-phorus combustion gas stream if the metal tempera~ure , 3~ ?
is maintained above the "meta~' acid dew point tempera-ture such that no condensation occurs. This re~uires metal temperatures above 500C. to 900C. depending on the combustion gas composition and pressure.
These temperatures would probably require the use of high temperature "re~ractory" alloys as materials of construction and the use of ~ases, fused salts or water at supercritical pressure as heat transfer media. The dirficulties involved in these approaches O are obvious to one skilled in the art.
Now, according to the present invention, it ~as surprisingly found that phosphorus pentoxide can be prepared under conditions ~herein the "meta" acid is relatively non-corrosive to a number of alloys at usefu~ steam generation temperatures. These alloys include the stainless steels commonly used in phos-phoric acid plants.
SUMMARY
These and other advantages are achieved by a process which comprises:
bringing together in a reaction zone elemental phosphorus and a sufficient amount of oxygen in a free-oxygen containing gas to form phosphorus pentoxide in a product stream while maintaining the mole ratio of water to phosphorus pentoxide to less than l:l in the product stream;
cooling the product stream from the reaction zone to a temperature not less than the dew point of any component in the produc~ stream b~y contacting the product stream with a metal cooling surface containing a heat trans~er ~luid to maintain the temperature o~ the metal cooling surface at least about 100C.; and recovering heat from the heat trans~er ~luid.
BRIEF DESCRIPTION OF THE DRAWING
The sole ~igure is a schematic representa-tion of one type of elemental phosphorus burning apparatus containing a means for removing heat from the products of the reaction zone and which illus-trates the process of the present lnvention.
DETAILED DESCRIPTION OF THE INVENTION
Turning now to the drawing, a free-oxygen containing gas is introduced into chamber 11 through line 12. Liquid elemental phosphorus is introduced through line 13 as a spray to react with the free-oxygen containing gas in the reaction zone contained in chamber 11. The ~ree-oxygen containing gas may contain some water, but the mole ratio of water to phosphorus pentoxide is maintained less than 1:1.
- 20 The product stream from khe reaction zone then passes through a crossover conduit lLI which contains a cooling surface 15. A heat transfer fluid is lntro-duced into cooling surface 15 through pipe 16 and exits cooling sur~ace 15 through exit pipe 17, where the heat in the heat transfer fluid can be utilized for other appllcations.
The remainder of the products of the reac-tion zone then pass through crossunder conduit 21 and are contacted with weak phosphoric acid or water ln absorber 22 which enters through scrub line 23. In absorber 22~ phosphorus pentoxide is converted to orthophosphoric acid. The remainder of the free-oxygen containing gas exits the system throu~gh exit conduit 24.
The free-oxygen containing gas useful in the process of the present invention can be derived from any number of sources. For example~ oxygen can be admixed with a noble gas such as neon, argon~
krypton, xenon and the like. On the other hand, air, nitrogen-enriched air or oxygen-enriched air can be used with satisfactory results~ but ordinary air is pre~erred. Since the reaction with elemen~al phos-phorus is very exothermic, the use of pure oxy~en should be avoided as well as free-oxygen containing gases containing greater than about 50 volume percent oxygen.
The amount of oxygen should be at least enough to react with the elemental phosphorus to form phosphorus pentoxide and it is preferred to use an excess amount of oxygen to avoid the formation o~ the lower oxides of phosphorus. For example, when air is used, about 30 percent more air than required to form phosphorus pentoxide should be introduced into the reaction chamber to avoid the formation of lower oxides of phosphorus. It is preferred to use at least about twice the stoichiometric amount of oxygen required to form phosphorus pentoxide and even as much as three times the stoichiometric amount of oxygen required to form phosphorus pentoxide. However3 when the free-oxygen - containing gas is air, greater than about three times the stoichiometric amount of oxygen required to form phosphorus pentoxide creates an excessively large amount o~ gas to handle and lowers the temperature of the product stream. Thus it is preferred to avoid using greater than about three times the stoichiometric amount of oxygen required to form phosphorus pentoxide.
It is important in the process of the present invention to maintain the mole ratio of water to phosphorus pentoxide less than 1 to 1. It is preferred to maintain the mole ratio of water to phosphorus pentoxide less than about 0.9 to 1, and even more preferred to maintain the mole ratio at less than about 0.5 to l to insure that corrosive polyphosphoric acid (i.e.~ acid containing a mole ratio of H2O to P2O5 of l:l or higher) is not formed-The amount of water in the process can readily be controlled by controlling the dew point of the free-oxygen containing gas entering the reac~
tion zone. At high humidities~ the amount of water can be controlled by drying the free-oxygen containing gas using conventional techniques. Alternatively the ratio of water to phosphorus pentoxide can be con-trolled by varying the amount of excess free-oxygen containing gas entering the reaction zone so that the moles of water entering the reaction zone relative to phosphorus pentoxide is maintained below l:l. A
combination of the two techniques can also be used.
As an example, the following tabulation shows mole percent phosphorus pentoxide in the mixture of phos-phorus pentoxide and water as a function of the dew point of air entering the reaction zone at a flow rate of 200 percent excess combustion air over that required to form P205.
H2O/P205 Mole Ratio As A Function Of Combustion Air Dew Point H20/P2O5 Dew Point Mole Ratio C._ F.
1.3 26.7 80 0.9 21,1 70 0.4 10 50 3 0.3 4~4 40 0.2 -l.l 30 Referring again to the drawing, cooling surface 15 can be any number of shapes~ sizes and configurations in order to remove heat from the product stream from the reaction zone. In addition, the cooling surface can be constructed of rather ordinary materials o~ construction, such as stainless ~teel, and this is what we prefer to use. The optimum size and con~iguration can be determined by those skilled in the art for their particular system, although we have found it convenient to use U-tubes or coils of stainless steel placed perpendicular to the flow of the product stream from the reaction zone.
The temperature of cooling surface 15 will depend upon a number of fac~ors as will occur to those skilled in the art. For example~ the particular heat transfer fluid employed, the configuration of the cooling sur~ace, its placement in the product stream~
khe temperature of the product stream, and other factors are all interrelated. It is preferred to maintain the temperature of the cooling sur~ace between about 150C. and abou~ 900C., preferably between about 200C. and about 300C.
Any number o~ heat trans~er ~luids can be introduced into cooling surface 15 through pipe 16 and exits from the cooling surface through exlt pipe 17. Suitable heat transfer fluids include gases, such as air, nitrogen, helium, neon, argon~ krypton and xenon and the like; water, including water at ordinary temperature and pressure, pressurized water, steam and the like; molten salt mixtures, such as a ternary mixture of approximately 16 percent by weight of lithium nitrate, 42 percent by weight of po~assium nitrate and Ll2 percent by weight of sodium nitrate, and the like; aromatlc and aliphatic organic compounds such as aniline, pyridine, thiophene and substituted derivatives thereof and aliphatic nitro compounds such as nitromethane and aliphatic nitriles and the like.
We prefer to use water at a temperature cf about 200C.
and at a pressure of about 35 atmospheres.
When the product stream from the reaction zone contacts the cooling surface, the product stream is cooled to a temperature not less than the ~ew point of any component in the product stream. The most likely components in the product stream to condense as the product stream is cooled are phosphorus pentoxide and ultraphosphoric acids (i.e.~ acids con-taining a mole ratio of H20 to P205 of less than 1:1). Hence, it is pre~erred to cool the product stream to a temperature not less than about 100C.
above the dew point of any component in the product stream. As will occur to those skilled in the art, the temperature of the cooled product stream ~ill depend upon a number of ~actors, such as the tempera-ture of the product stream leaving the reaction zone, the temperature of the cooling surface, the efficiency o~ the coollng surface, and the like, and the tempera-ture of the cooled product stream can readily be con-trolled throùgh routine experimentation for any particular ~acility.
Even though the temperature of the cooled product stream is above the dew point of any component in the product stream, some of the components, such as ultraphosphoric acid and/or phosphorus pentoxide, can condense on the cooling surface. This is no problem in the process of the present invention since excess condensate will be removed by the product stream having a temperature above the dew point of the con-densate. Indeed, a film of condensate on the cooling surface tends to relieve heat stress in the metal created by the heat transfer fluid on one side and the hot product stream on the other. As long as the water to phosphorus pentoxide mole ratio is less than l:l, the corrosion on the cooling surface is minimal.
The valuable heat contained in the heat transfer fluid can be recovered and economically used by conventional techniques known to those skilled in the art. For example, the heat transfer fluid from g exit pipe 17 can be used to heat water to make steam for other chemical processes, to generate electricity, and the like. On the other hand, if pressurized water is used as the heat transfer fluid, it can be used directly to make high pressure steam for the above purposes, although it may be desirable to maintain this water in a closed system. After the heat ~rom the heat trans~er fluid in a closed system has been removed for other uses, the heat transfer ~luid can be introduced again into cooling sur~ace 15 through pipe 16. Other modifications and uses will occur to those skilled in the art in view of the present disclosure.
The invention is further illustrated by but not limited to the following sole Example wherein all proportions are by weight unless otherwise indi-cated.
EXAMPLE I
An elemental phosphorus burner is modi~ied b~ placing a 316 stainless steel U-tube in the cross-over conduit perpendicular to the flow of gases from the burning chamber. Pressurized water at a pressure of 35 atmospheres is circulated through the U-tube.
Then3 about 7,70U kilograms per hour of air are intro-duced into the burning chamber, and then about 454kilograms per hour of molten elemental phosphorus are sprayed into the air from above. The dew point of the air is about ~C. The temperature of the water circulating through the U-tube increases to about 200C. and su~ficient water flow is maintained in the U-tube to maintain this temperature. About 62,000 kilocalories per hour per square meter of cooling surface are recovered as steam for other uses.
Although the invention has been described in specified embodiments which are set forth in considerable detail, it should be understood that this is by ~ay o~ illustration only, and that the inven-tion is nok necessarily limited thereto, since alternative embodiments and operating techniques will . become apparent to those skilled in the art in view of the disclosure. As an example, the invention has been illustrated with respect to one design o~ a facility to convert elemental phosphorus to phosphorus pentoxide wherein the product stream from the reactor chamber passes through a refractory-lined crossover conduit. As is known to those skilled in the art, - some ~acilities use crossunder conduits rather than crossover conduits, and some facilities have yet other configurations. In some facilities, the walls can be cooled with fluids, such as air or water, to recover usable heat in addition to the process described herein, and all such designs are deemed to be equivalent to the design described herein for purposes of this invention. Accordingly, modi~ica~
tions are contemplated which can be made without departing from the spirit of thé described invention.
3_4575 RECOVERING HEAT FROM
BURNING ELEMENTAL PHOSPHORUS
~ BACKGROUND OF THE INVENTION
This inventlon relates to a process for 5 recoverin~ valuable ener~y ~rom burning of phosphorus.
Phosphorus pentoxide is an important chemical intermediate used to prepare phosphoric acid and many other phosphorus-containing compounds. Indeed, millions of kilograms of phosphorus pentoxide are produced each year to prepare phosphoric acid for a wide variety of applications.
As is known to those skilled in the art, phosphorus pentoxide is prepared commercially by burning elemental phosphorus in a stream of dried air.
Adequate time is allowed to complete the reaction to prevent the ~ormation of lower oxldes of phosphorus.
The resulting phosphorus pentoxide can be made so free o~ lower oxides that it will not decolorize dilute permanganate solutions. The usual plant for manu-~acturing phosphorus pento~ide consists o~ a phosphorusfeed systemg provisions for drying the air, a burning chamber, and a mechanism to collect the phosphorus pentoxide. On the other hand, when phosphoric acid is the only desired end product, the air is not usually dried, and the phosphorus pentoxide is contacted with water to form the phosphoric acid.
The oxidation o~ elemental phosphorus with oxygen evolves about 5.8 million calories per kilo-gram of phosphorus. The temperatures of the gases ~rom the oxidation vary ~rom about 90oC. up to about 3,000C., dependin~ on the amount of excess gases used in the process.
Despite the presence of so much available heat from the process, this heat has not heretofore been recovered and used efficiently. The only known commercial uses of waste heat from phosphorus combus-tion are for preheating combustion air for another process by heat transfer through a re~ractory protected - wall, or for evaporation of water from soda ash solu-tions by using the solutions in the hydrator/absorber and mist collection circuits in the acid process.
The prior art on production of phosphoric acid ~rom elemental phosphorus abounds with references to the disastrous corrosive attack of the acid on metals at temperatures well below those necessary for generation of steam at useful distribution pressures. ~he condensation of polymeric acids on hot metal surfaces was thought to be particularly corrosive. The polymeric acids were commonly called '7meta acid", a term used loosely to describe any polymeric acid composition that is not fluid at room temperature. Such compositions are those above about 85 percent P205. To avoid this corrosive attack, metal surfaces were either protected by a layer of refractory material, or maintained below 100C. where the corrosion rate is tolerable on stainless steels commonly used in phosphoric acid plants. Neither of these methods are attractive for recovery of heat at useful steam distribution pressures.
It has been speculated without proof for years that heat could be recovered from the phos-phorus combustion gas stream if the metal tempera~ure , 3~ ?
is maintained above the "meta~' acid dew point tempera-ture such that no condensation occurs. This re~uires metal temperatures above 500C. to 900C. depending on the combustion gas composition and pressure.
These temperatures would probably require the use of high temperature "re~ractory" alloys as materials of construction and the use of ~ases, fused salts or water at supercritical pressure as heat transfer media. The dirficulties involved in these approaches O are obvious to one skilled in the art.
Now, according to the present invention, it ~as surprisingly found that phosphorus pentoxide can be prepared under conditions ~herein the "meta" acid is relatively non-corrosive to a number of alloys at usefu~ steam generation temperatures. These alloys include the stainless steels commonly used in phos-phoric acid plants.
SUMMARY
These and other advantages are achieved by a process which comprises:
bringing together in a reaction zone elemental phosphorus and a sufficient amount of oxygen in a free-oxygen containing gas to form phosphorus pentoxide in a product stream while maintaining the mole ratio of water to phosphorus pentoxide to less than l:l in the product stream;
cooling the product stream from the reaction zone to a temperature not less than the dew point of any component in the produc~ stream b~y contacting the product stream with a metal cooling surface containing a heat trans~er ~luid to maintain the temperature o~ the metal cooling surface at least about 100C.; and recovering heat from the heat trans~er ~luid.
BRIEF DESCRIPTION OF THE DRAWING
The sole ~igure is a schematic representa-tion of one type of elemental phosphorus burning apparatus containing a means for removing heat from the products of the reaction zone and which illus-trates the process of the present lnvention.
DETAILED DESCRIPTION OF THE INVENTION
Turning now to the drawing, a free-oxygen containing gas is introduced into chamber 11 through line 12. Liquid elemental phosphorus is introduced through line 13 as a spray to react with the free-oxygen containing gas in the reaction zone contained in chamber 11. The ~ree-oxygen containing gas may contain some water, but the mole ratio of water to phosphorus pentoxide is maintained less than 1:1.
- 20 The product stream from khe reaction zone then passes through a crossover conduit lLI which contains a cooling surface 15. A heat transfer fluid is lntro-duced into cooling surface 15 through pipe 16 and exits cooling sur~ace 15 through exit pipe 17, where the heat in the heat transfer fluid can be utilized for other appllcations.
The remainder of the products of the reac-tion zone then pass through crossunder conduit 21 and are contacted with weak phosphoric acid or water ln absorber 22 which enters through scrub line 23. In absorber 22~ phosphorus pentoxide is converted to orthophosphoric acid. The remainder of the free-oxygen containing gas exits the system throu~gh exit conduit 24.
The free-oxygen containing gas useful in the process of the present invention can be derived from any number of sources. For example~ oxygen can be admixed with a noble gas such as neon, argon~
krypton, xenon and the like. On the other hand, air, nitrogen-enriched air or oxygen-enriched air can be used with satisfactory results~ but ordinary air is pre~erred. Since the reaction with elemen~al phos-phorus is very exothermic, the use of pure oxy~en should be avoided as well as free-oxygen containing gases containing greater than about 50 volume percent oxygen.
The amount of oxygen should be at least enough to react with the elemental phosphorus to form phosphorus pentoxide and it is preferred to use an excess amount of oxygen to avoid the formation o~ the lower oxides of phosphorus. For example, when air is used, about 30 percent more air than required to form phosphorus pentoxide should be introduced into the reaction chamber to avoid the formation of lower oxides of phosphorus. It is preferred to use at least about twice the stoichiometric amount of oxygen required to form phosphorus pentoxide and even as much as three times the stoichiometric amount of oxygen required to form phosphorus pentoxide. However3 when the free-oxygen - containing gas is air, greater than about three times the stoichiometric amount of oxygen required to form phosphorus pentoxide creates an excessively large amount o~ gas to handle and lowers the temperature of the product stream. Thus it is preferred to avoid using greater than about three times the stoichiometric amount of oxygen required to form phosphorus pentoxide.
It is important in the process of the present invention to maintain the mole ratio of water to phosphorus pentoxide less than 1 to 1. It is preferred to maintain the mole ratio of water to phosphorus pentoxide less than about 0.9 to 1, and even more preferred to maintain the mole ratio at less than about 0.5 to l to insure that corrosive polyphosphoric acid (i.e.~ acid containing a mole ratio of H2O to P2O5 of l:l or higher) is not formed-The amount of water in the process can readily be controlled by controlling the dew point of the free-oxygen containing gas entering the reac~
tion zone. At high humidities~ the amount of water can be controlled by drying the free-oxygen containing gas using conventional techniques. Alternatively the ratio of water to phosphorus pentoxide can be con-trolled by varying the amount of excess free-oxygen containing gas entering the reaction zone so that the moles of water entering the reaction zone relative to phosphorus pentoxide is maintained below l:l. A
combination of the two techniques can also be used.
As an example, the following tabulation shows mole percent phosphorus pentoxide in the mixture of phos-phorus pentoxide and water as a function of the dew point of air entering the reaction zone at a flow rate of 200 percent excess combustion air over that required to form P205.
H2O/P205 Mole Ratio As A Function Of Combustion Air Dew Point H20/P2O5 Dew Point Mole Ratio C._ F.
1.3 26.7 80 0.9 21,1 70 0.4 10 50 3 0.3 4~4 40 0.2 -l.l 30 Referring again to the drawing, cooling surface 15 can be any number of shapes~ sizes and configurations in order to remove heat from the product stream from the reaction zone. In addition, the cooling surface can be constructed of rather ordinary materials o~ construction, such as stainless ~teel, and this is what we prefer to use. The optimum size and con~iguration can be determined by those skilled in the art for their particular system, although we have found it convenient to use U-tubes or coils of stainless steel placed perpendicular to the flow of the product stream from the reaction zone.
The temperature of cooling surface 15 will depend upon a number of fac~ors as will occur to those skilled in the art. For example~ the particular heat transfer fluid employed, the configuration of the cooling sur~ace, its placement in the product stream~
khe temperature of the product stream, and other factors are all interrelated. It is preferred to maintain the temperature of the cooling sur~ace between about 150C. and abou~ 900C., preferably between about 200C. and about 300C.
Any number o~ heat trans~er ~luids can be introduced into cooling surface 15 through pipe 16 and exits from the cooling surface through exlt pipe 17. Suitable heat transfer fluids include gases, such as air, nitrogen, helium, neon, argon~ krypton and xenon and the like; water, including water at ordinary temperature and pressure, pressurized water, steam and the like; molten salt mixtures, such as a ternary mixture of approximately 16 percent by weight of lithium nitrate, 42 percent by weight of po~assium nitrate and Ll2 percent by weight of sodium nitrate, and the like; aromatlc and aliphatic organic compounds such as aniline, pyridine, thiophene and substituted derivatives thereof and aliphatic nitro compounds such as nitromethane and aliphatic nitriles and the like.
We prefer to use water at a temperature cf about 200C.
and at a pressure of about 35 atmospheres.
When the product stream from the reaction zone contacts the cooling surface, the product stream is cooled to a temperature not less than the ~ew point of any component in the product stream. The most likely components in the product stream to condense as the product stream is cooled are phosphorus pentoxide and ultraphosphoric acids (i.e.~ acids con-taining a mole ratio of H20 to P205 of less than 1:1). Hence, it is pre~erred to cool the product stream to a temperature not less than about 100C.
above the dew point of any component in the product stream. As will occur to those skilled in the art, the temperature of the cooled product stream ~ill depend upon a number of ~actors, such as the tempera-ture of the product stream leaving the reaction zone, the temperature of the cooling surface, the efficiency o~ the coollng surface, and the like, and the tempera-ture of the cooled product stream can readily be con-trolled throùgh routine experimentation for any particular ~acility.
Even though the temperature of the cooled product stream is above the dew point of any component in the product stream, some of the components, such as ultraphosphoric acid and/or phosphorus pentoxide, can condense on the cooling surface. This is no problem in the process of the present invention since excess condensate will be removed by the product stream having a temperature above the dew point of the con-densate. Indeed, a film of condensate on the cooling surface tends to relieve heat stress in the metal created by the heat transfer fluid on one side and the hot product stream on the other. As long as the water to phosphorus pentoxide mole ratio is less than l:l, the corrosion on the cooling surface is minimal.
The valuable heat contained in the heat transfer fluid can be recovered and economically used by conventional techniques known to those skilled in the art. For example, the heat transfer fluid from g exit pipe 17 can be used to heat water to make steam for other chemical processes, to generate electricity, and the like. On the other hand, if pressurized water is used as the heat transfer fluid, it can be used directly to make high pressure steam for the above purposes, although it may be desirable to maintain this water in a closed system. After the heat ~rom the heat trans~er fluid in a closed system has been removed for other uses, the heat transfer ~luid can be introduced again into cooling sur~ace 15 through pipe 16. Other modifications and uses will occur to those skilled in the art in view of the present disclosure.
The invention is further illustrated by but not limited to the following sole Example wherein all proportions are by weight unless otherwise indi-cated.
EXAMPLE I
An elemental phosphorus burner is modi~ied b~ placing a 316 stainless steel U-tube in the cross-over conduit perpendicular to the flow of gases from the burning chamber. Pressurized water at a pressure of 35 atmospheres is circulated through the U-tube.
Then3 about 7,70U kilograms per hour of air are intro-duced into the burning chamber, and then about 454kilograms per hour of molten elemental phosphorus are sprayed into the air from above. The dew point of the air is about ~C. The temperature of the water circulating through the U-tube increases to about 200C. and su~ficient water flow is maintained in the U-tube to maintain this temperature. About 62,000 kilocalories per hour per square meter of cooling surface are recovered as steam for other uses.
Although the invention has been described in specified embodiments which are set forth in considerable detail, it should be understood that this is by ~ay o~ illustration only, and that the inven-tion is nok necessarily limited thereto, since alternative embodiments and operating techniques will . become apparent to those skilled in the art in view of the disclosure. As an example, the invention has been illustrated with respect to one design o~ a facility to convert elemental phosphorus to phosphorus pentoxide wherein the product stream from the reactor chamber passes through a refractory-lined crossover conduit. As is known to those skilled in the art, - some ~acilities use crossunder conduits rather than crossover conduits, and some facilities have yet other configurations. In some facilities, the walls can be cooled with fluids, such as air or water, to recover usable heat in addition to the process described herein, and all such designs are deemed to be equivalent to the design described herein for purposes of this invention. Accordingly, modi~ica~
tions are contemplated which can be made without departing from the spirit of thé described invention.
Claims (12)
- The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
l. A process which comprises:
(a) bringing together in a reaction zone elemental phosphorus and a sufficient amount of oxygen in a free-oxygen containing gas to form phosphorus pentoxide in a product stream while maintaining a mole ratio of water to phos-phorus pentoxide to less than 1:1 in the product stream;
(b) cooling the product stream from the reaction zone to a tempera-ture not less than the dew point of any component in the product stream by contacting the product stream with a metal cooling surface containing a heat transfer fluid to maintain the temperature of the metal cooling sur-face at least about 100°C.; and (c) recovering heat from the heat transfer fluid. - 2. A process of Claim 1 wherein the amount of oxygen is at least about twice the stoichiometric amount required to form phosphorus pentoxide.
- 3. A process of Claim 1 wherein the amount of oxygen is between about twice and about three times the stoichiometric amount required to form phosphorus pentoxide.
- 4. A process of Claim 1 wherein the mole ratio of water to phosphorus pentoxide is less than about 0.9:1.
- 5. A process of Claim 1 wherein the product stream is cooled to a temperature not less than about 100°C. above the dew point of any component in the product stream.
- 6. A process of Claim 5 wherein the cooling surface is maintained between about 150°C. and about 900°C.
- 7. A process of Claim 5 wherein the cooling surface is maintained between about 200°C.
and about 300°C. - 8. A process of Claim 1 wherein the heat transfer fluid is selected from the group consisting of noble gases, free-nitrogen containing gases, eutectic salt mixtures, water and steam.
- 9. A process of Claim 8 wherein the heat transfer fluid is pressurized water.
- 10. A process of Claim 8 wherein the metal cooling surface is a U-tube.
- 11. A process of Claim 10 wherein the metal cooling surface is a stainless steel coil.
- 12. A process which comprises:
(a) bringing together in a reaction zone elemental phosphorus and at least twice the stoichiometric amount of oxygen in a free-oxygen containing gas to form phosphorus pentoxide, to provide a product stream having a mole ratio of water to phosphorus pentoxide of less than about 0.6 to 1;
(b) cooling the product stream from the reaction zone to a temperature not less than about 100°C. above the dew point of any component in the product stream by contacting the product stream with a stainless steel cooling coil containing pressurized water as a heat transfer fluid to maintain the cooling coil at a temperature between about 200°C.
and about 900°C.; and (c) recovering heat from the pressurized water.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US13876280A | 1980-04-09 | 1980-04-09 | |
| US138,762 | 1980-04-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1139099A true CA1139099A (en) | 1983-01-11 |
Family
ID=22483529
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000375026A Expired CA1139099A (en) | 1980-04-09 | 1981-04-08 | Recovering heat from burning elemental phosphorus |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS56155009A (en) |
| CA (1) | CA1139099A (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100397023C (en) * | 2003-01-04 | 2008-06-25 | 胡云北 | Method forrecovering heat quantity carried by yellow phosphorus waste slag and heat quantity produced by reaction tail gas and their comprehensive utilization |
| EP2053034B1 (en) | 2003-11-20 | 2018-01-24 | Solvay Sa | Process for producing a chlorohydrin |
| BRPI0618325A2 (en) * | 2005-11-08 | 2011-08-23 | Solvay | process stop dichloropropanol production |
| EP2621911A1 (en) | 2010-09-30 | 2013-08-07 | Solvay Sa | Derivative of epichlorohydrin of natural origin |
| US12016977B2 (en) | 2017-10-06 | 2024-06-25 | Dsm Ip Assets B.V. | Method of making an osteoconductive fibrous article and a medical implant comprising such osteoconductive fibrous article |
-
1981
- 1981-04-08 CA CA000375026A patent/CA1139099A/en not_active Expired
- 1981-04-08 JP JP5193381A patent/JPS56155009A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| JPS56155009A (en) | 1981-12-01 |
| JPS6339522B2 (en) | 1988-08-05 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry | ||
| MKEX | Expiry |
Effective date: 20000111 |