GB1603630A – Gas-liquid contact process
– Google Patents
GB1603630A – Gas-liquid contact process
– Google Patents
Gas-liquid contact process
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Publication number
GB1603630A
GB1603630A
GB25269/77A
GB2526977A
GB1603630A
GB 1603630 A
GB1603630 A
GB 1603630A
GB 25269/77 A
GB25269/77 A
GB 25269/77A
GB 2526977 A
GB2526977 A
GB 2526977A
GB 1603630 A
GB1603630 A
GB 1603630A
Authority
GB
United Kingdom
Prior art keywords
air
oxygen
bleaching
zone
gas
Prior art date
1977-06-16
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB25269/77A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BOC Ltd
Original Assignee
BOC Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
1977-06-16
Filing date
1977-06-16
Publication date
1981-11-25
1977-06-16
Application filed by BOC Ltd
filed
Critical
BOC Ltd
1977-06-16
Priority to GB25269/77A
priority
Critical
patent/GB1603630A/en
1978-06-15
Priority to IE1207/78A
priority
patent/IE47094B1/en
1978-06-15
Priority to IT24595/78A
priority
patent/IT1096666B/en
1978-06-15
Priority to ES470814A
priority
patent/ES470814A1/en
1978-06-15
Priority to FR7817952A
priority
patent/FR2394493A1/en
1978-06-15
Priority to US05/915,861
priority
patent/US4183906A/en
1978-06-15
Priority to DE19782826143
priority
patent/DE2826143A1/en
1978-06-16
Priority to AU37181/78A
priority
patent/AU517218B2/en
1978-06-16
Priority to NLAANVRAGE7806528,A
priority
patent/NL188033C/en
1978-06-16
Priority to BE188643A
priority
patent/BE868207A/en
1981-11-25
Publication of GB1603630A
publication
Critical
patent/GB1603630A/en
Status
Expired
legal-status
Critical
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Classifications
C—CHEMISTRY; METALLURGY
C01—INORGANIC CHEMISTRY
C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
C01B21/00—Nitrogen; Compounds thereof
C01B21/20—Nitrogen oxides; Oxyacids of nitrogen; Salts thereof
C01B21/24—Nitric oxide (NO)
C01B21/26—Preparation by catalytic or non-catalytic oxidation of ammonia
Description
PATENT SPECIFICATION ( 11) 1 603 630
( 21) Application No 25269/77 ( 22) Filed 16 Jun 1977 ( 19) ( 23) Complete Specification Filed 31 May 1978 ( 44) Complete Specification Published 25 Nov 1981 < ( 51) INT CL 3 C Oi B 21/40 Z ( 52) Index at Acceptance S Ci A 213 ( 72) Inventors: PHILIP GARY BLAKEY \ RICHARD WILLIAM WATSON ( 54) GAS-LIQUID CONTACT PROCESS ( 71) We, BOC LIMITED of Hammersmith House, London W 6 9 DX, England, an English company, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in
and by the following statement:
This invention relates to a gas-liquid contact process for producing nitric acid from a gas 5 mixture formed by the catalytic oxidation of ammonia One conventional process for making nitric acid includes the steps of oxidising ammonia by air to nitric oxide and water vapour in a catalytic burner (the catalyst typically being platinum/rhodium) at a temperature in the order of 900 'C.
The reaction products from the burner typically contain 9 % by volume of nitric oxide, 10 % by volume of nitrogen, 14 % by volume of water and 7 % by volume of oxygen They are cooled, typically in two stages, to below a temperature at which the water vapour condenses Reaction between the water and the nitric oxide and oxygen results in the condensate being a dilute solution of nitric acid First, nitric oxide reacts with oxygen to form nitrogen dioxide which is an equilibrium with its dimer dinitrogen tetroxide Then, the 15 nitrogen dioxide reacts with the water to form nitric acid.
The unreacted gases are passed into the bottom section of at least one absorption column or other gas/liquid contact device in which the ascending gases are contacted with a descending flow of water The dilute nitric acid from the condenser is introduced into the or each column at an intermediate level 20 The nitric oxide reacts with oxygen from the air in the or each column to form dinitrogen tetroxide which reacts with water to form nitric acid Accordingly, as the water descends the or each column so it becomes richer in nitric acid The product leaving the bottom of the column typically contains from 50 to 70 % by weight of nitric acid.
It is found, however, that this product tends typically to have dissolved impurities in it 25 owing to the presence of unoxidised nitric oxide and/or nitrous acid in it The nitric acid may, therefore be passed into the top of at least one so-called "bleaching tower" in which it is contacted by an ascending stream of air effective to remove the discolouration The gas leaving the top of the or each "bleaching tower" is returned to the or each absorption column 30 If desired, one or more columns, the or each of which perform both the absorption and bleaching functions may be employed.
The absorption columns and other parts of the plant may be operated at just above atmospheric pressure ( 1 3 to 1 5 bar), medium pressure (ie 3 to 6 bar) or high pressure ( 8 to 12 bar) 35 According to the present invention there is provided a gas-liquid contact process for making nitric acid including the steps of:
(a) reacting primary air and ammonia catalytically at elevated temperature to form a gas comprising nitric oxide, nitrogen, oxygen and water vapour; (b) cooling the gas to a temperature at which water vapour condenses; 40 (c) introducing the cooled gas into one or more columnar absorption zones and contacting it countercurrently with water and thereby forming product nitric acid; (d) passing the product nitric acid into a bleaching zone wherein bleaching air is passed through the product nitric acid; (e) enriching the bleaching air in oxygen, in, upstream of, or downstream of, the 45 2 1,603,630 2 bleaching zone; (f) passing secondary air through the or each absorption zone with the cooled gas, the secondary air being constituted at least in part by the oxygen-enriched bleaching air; (g) enriching in oxygen the gas passing through the absorption zone(s) at one or more regions where the absorption reaction is from 50 to 90 % complete 5 By the expression 'the absorption reaction is from 50 to 90 % complete' we mean that 50 to 90 % by weight of the oxides of nitrogen in the gas entering the absorption zone or zones has been converted to nitric acid.
The process according to the invention makes it possible to achieve particularly favourable conditions in the absorption zone or zones for the chemical reactions that take 10 place These reactions are:
3 NO, + H,0 = 2 HNO 3 + NO and 2 NO + 02 = 2 N 02 = N 204 15 When the cooled gas first comes into contact with water in the absorption zone or zones (ie the absorption reaction has not begun) we believe that provided the oxidation ratio of the gas is low, the residence time of the gas (which is inversely proportional to its velocity) is a more critical parameter than the oxygen partial pressure.
On the other hand, as the absorption reaction progresses more nitric oxide is formed and 20 the partial pressure of oxygen in the gas becomes more critical The process according to the present invention makes it possible to optimise the gas velocities and oxygen partial pressures in different regions of the absorption zone or zones.
By a low oxidation ratio we mean one in the order of 0 05 to 0 4, the oxidation ratio being expressed as 25 NO NO + NO 2 where NO represents the number of moles of nitric oxide in the gas entering the absorption 30 zone, or the first absorption zone if there are more than one, and NO 2 represents the number of moles of nitrogen dioxide in the gas entering the said absorption zone For the purpose of the oxidation ratio, each mole of dinitrogen tetroxide is treated as consisting of two moles of nitrogen dioxide.
A conventional plant for making nitric acid can readily be adapted to perform the process 35 according to the invention By making such a conversion it is possible to decrease the concentration of oxides of nitrogen in the gas vented from the absorption zone or zones, to increase the rate of production of nitric acid without increasing the concentration of oxides of nitrogen in the gas vented from the absorption zone or zones, or to increase the concentration of the product nitric acid without increasing the concentration of oxides of 40 nitrogen in the gas vented from the absorption zone or zones.
Accordingly, the invention also provides a method of improving a process for making nitric acid, the process including the steps of:
(a) reacting primary air and ammonia catalytically at elevated temperature to form a gas comprising nitric oxide, nitrogen, oxygen and water vapour; 45 (b) cooling the gas to a temperature at which the water vapour condenses; (c) introducing the cooled gas into one or more columnar absorption zones and contacting it countercurrently with water and thereby forming product nitric acid; (d) passing the product nitric acid into a bleaching zone wherein bleaching air is passed through the product nitric acid; 50 (e) passing secondary air through the or each absorption zone with the cooled gas, the secondary air being formed at least in part by bleaching air taken from the bleaching zone; the improvement being effected by:
1 making a reduction in the rate at which the bleaching air or other air is taken to form the secondary air; 55 2 enriching in oxygen the bleaching air upstream of, in, or downstream of the bleaching zone; 3 enriching in oxygen the gas passing through the absorption zone or zones at one or more regions where the absorption reaction is from 50 to 90 % complete, and thereby performing the process according to the invention 60 The temperature at which the catalytic reaction between ammonia and air is performed is typically the same as that at which it is performed in known processes eg between 830 and 950 'C The catalyst is typically a platinum-rhodium catalyst.
The gas from the catalytic reaction zone(s) is typically cooled by being passed through at least two heat exchangers In the heat exchangers oxygen in the gas reacts with the nitric 65 1,603,630 oxide to form nitrogen dioxide which is tautomeric equilibrium with its dimer dinitrogen tetroxide The more or most downstream heat exchanger will typically be adapted to function as a condenser, in which, in operation of the process, the water vapour condenses.
The nitrogen dioxide will react with the condensate to form a dilute solution of nitric acid and nitric oxide The so-formed dilute nitric acid is typically introduced into the absorption 5 zone or zones at one or more chosen locations and becomes united with the nitric acid being formed in the absorption zone or zones Typically, the gas is cooled to a temperature at or near to ambient (ie between 0 and 1000 C) Preferably it is cooled to 40 to 80 TC.
In the or each absorption zone gas-liquid contact surfaces are typically provided by sieve trays along which liquid flows in operation of the process, descending from tray-to-tray and 10 contacting gas ascending through apertures in the trays It is possible, however, to use other devices to provide thorough contact between the gas and liquid For example, bubble-cap trays may be used to provide gas-liquid contact surfaces.
There may be one or more absorption zones If there is just one absorption zone, water (substantially pure or containing nitric acid in solution) may be introduced into the top of 15 the zone and the cooled gas and secondary air at the bottom of the zone As the water descends the zone (or column) so it becomes progressively richer in nitric acid, while as the united cooled gas and secondary air ascends so progressively more of its nitrogen dioxide (or dinitrogen tetroxide) takes part in the absorption reaction to form nitric acid.
Moreover, as the gas ascends the absorption zone, nitric oxide reformed by the absorption 20 reaction is reconverted into nitrogen dioxide which is subsequently absorbed By the time the gas reaches the top of the absorption zone, substantially all the oxides of nitrogen have been removed therefrom The remaining gas is typically vented to the atmosphere.
Instead of there being just one absorption zone there may be a series of such zones In the first zone encountered by the cooled gas and secondary air by no means all of the oxides of 25 nitrogen are removed from the gas Thus, the gas leaving the top of the first absorption zone is taken from this zone and passed into the bottom of a second absorption zone, and so one until substantially all the oxides of nitrogen are removed therefrom Typically water is introduced into the top of the last zone encountered by the gas, and the resultant dilute nitric acid collecting at the bottom of this zone passed into the next-tolast zone, and so on 30 Thus, the product nitric acid is collected at the bottom of the first zone.
The bleaching zone may be situated within a column or tower separate from the absorption zone(s) (or column(s)) Alternatively, it is possible to provide the bleaching zone within the same column as that which defines the absorption zone, or, if there is more than one absorption zone, the same column as that in which the product nitric acid is 35 collected If a single column defines both an absorption zone and a bleaching zone, the cooled gas will not be introduced right at the bottom of this column, but, instead, some distance up Thus, the level at which the cooled gas is introduced defines the boundary between the absorption zone and the bleaching zone in that column In such an instance, the bleaching air would typically be enriched in oxygen upstream of the bleaching zone 40 (with reference to the flow of gas), and the secondary air would typically be formed entirely of the oxygen-enriched bleaching air.
The bleaching air, so it is believed, performs two main functions The first is to strip dissolved gases from the product nitric acid The second is to oxidise impurities in the product nitric acid Thus the bleaching air is able to remove discolouration (if any) from the 45 product nitric acid.
The bleaching air is preferably enriched in oxygen upstream of (with reference to the flow of gas) (or in) the bleaching zone Preferably, the bleaching air is enriched in oxygen to form a gas mixture containing from 25 to 45 % by volume of oxygen Preferably, the oxygen is used to enrich the bleaching air is commercial oxygen by which is meant pure oxygen or a 50 gas mixture containing at least 90 % by volume of oxygen Alternatively oxygen-enriched air containing at least 40 % by volume of oxygen may be used.
The main advantage of enriching the bleaching air in oxygen upstream of (with reference to the flow of gas) or in the bleaching zone is that it makes possible the selection of a rate of feeding secondary air into the absorption zone or zones which can give favourable residence 55 times (or gas velocities) and oxygen partial pressures at the bottom of the column This is perhaps best illustrated by reference to the conversion of a conventional process to one in accordance with the invention Since the effective bleaching of the product nitric acid is in part dependent on the rate at which oxygen passes through the bleaching zone, the rate at which the bleaching air enters the bleaching zone may be reduced without the rate at which 60 oxygen passes therethrough being substantially altered Consequently the rate at which secondary air enters the absorption zone or zones is reduced This makes it possible to achieve a reduction in the gas velocity of the cooled gas and secondary air entering the column Hence, it is possible to increase the residence time of the gases in the first part of the absorption zone or zones This, as aforementioned, is a favourable change to make in 65 1,603,630 the part of the absorption zone or zones which is first encountered by the cooled gas.
Moreover, an increase in the partial pressure of oxygen in this part of the column can be achieved.
Since in most existing plants the primary air and the bleaching air are taken from the same compressor (or bank of compressors), reducing the rate at which the bleaching air is 5 used makes it possible to reduce the load on the compressor or compressors and hence the power consumed or to increase the rate at which air is passed into the catalytic reaction zone in which the oxidation of ammonia takes place It is thus possible to produce more nitric oxide in the reaction zone by correspondingly increasing the rate at which ammonia is fed into the reaction zone Thus, by adopting the process according to the invention, it is 10 possible to increase the rate at which oxides of nitrogen enter the absorption zone or zones.
Irrespective of whether or not the rate at which oxides of nitrogen enters the absorption zone or zones is increased an increase in the residence time of the gases in the first part of the absorption zone or zones will increase the extent to which the absorption reaction takes place in the bottom of the absorption zone or in the first absorption zone (if there is more 15 than one absorption zone) Addition of commercial oxygen (ie pure oxygen or gas mixture containing at least 90 % by volume of oxygen) or oxygen-enriched air to the gas passing through the absorption zone or zones makes it possible to reconvert to nitrogen dioxide substantially all the nitric oxide formed as a result of the absorption reaction This oxygen is added at one or more regions where the absorption reaction is from 50 to 90 % complete 20 (having regard to the quantity of oxides of nitrogen in the gas at such region or regions in comparison to the quantity in the cooled gas entering the absorption zone or zones) At such regions the residence time of the gas is not such a critical parameter as the partial pressure of oxygen, so it is possible to make relatively large increases in the partial pressure of oxygen there 25 The amount per unit time of oxygen that is required to be added at such region will depend on whether or not the rate at which oxides of nitrogen enter the absorption zone or zones is increased If this rate is not increased and it is the intention to reap the advantage of the oxygen additions by a reduction in the concentrtation of oxides of nitrogen in the gas vented from the absorption zone or zones, typically 1 volume of oxygen may be added to 30 the gas passing through the absorption zone or zones for each 9 to 10 volumes of extra oxygen added to the bleaching air If, however, the rate at which oxides of nitrogen enter the absorption zone or zones is increased, typically up to 4 volumes of oxygen may be added to the gas passing through the absorption zone or zones for each 6 volumes of extra oxygen added to the bleaching air 35 An increase in the rate at which oxides of nitrogen enter the absorption zone or zones may be exploited by increasing the concentration of the product acid, or by increasing the rate of production of product acid, or by obtaining both advantages.
The increase in the rate of production of nitric acid may be achieved by increasing the rate at which water is passed through the absorption zone or zones 40 If no such increase in the rate at which water is passed through the absorption zone or zones is made then an increase in the concentration of the product nitric acid may be achieved Indeed, it may be possible to reduce the rate at which water is passed through the absorption zone or zones and thereby achieve an even larger increase in the concentration of the product nitric acid Both the increase in the rate of production of acid and/or the 45 increase in its concentration can be achieved without increasing the concentration of oxides of nitrogen in the gas vented from the absorption zone or zones.
Since the process according to the invention makes it possible to reduce the rate at which bleaching air is taken to form the secondary air, it is possible to increase the ratio of primary air to secondary air when converting an existing process to one in accordance with the 50 present invention In absolute terms, if the oxygen-enriched bleaching air contains 25 to % by volume of oxygen, the ratio:
AR + AF AB + AE + Ap 55 expressed as a percentage is preferably in the range 5 to 12 % wherein:
AB represents the rate (mass per unit time) at which air is taken to form the bleaching air; AE represents the rate (mass per unit time) at which air is added to the bleaching air to form the secondary air, and 60 Ap represents the rate (mass per unit time) at which the primary air enters the catalytic reaction zone(s).
Preferably this ratio is in the range 5 to 8 %.
Typically, no extra air needs to be added to the bleaching air to form the secondary air (ie AF=O) However, if a plant for performing a conventional process has a pipe for supplying 65 1,603,630 such additional air to the absorption zone or zones, it is possible to reduce the rate at which such additional air is supplied rather than reducing the rate at which bleaching air is supplied to the absorption zone or zones Moreover, the oxygen (typically pure) or oxygen-enriched air used to enrich the bleaching air may be premixed with the additional air that is added to the bleaching air to form the secondary air However, this is not 5 preferred Moreover, in many if not most, plants such additional air from the atmosphere is not employed.
Preferably, commercial oxygen (as hereinbefore defined) used to enrich in oxygen the gas passing through the absorption zone or zones, is introduced into such zone or zones at a rate in the range of 2 to 15 %: of that at which the cooled gas enters the absorption zone or 10 zones.
Preferably, the gas passing through the absorption zone or zones is enriched in oxygen at one or more regions where the absorption reaction is from 70 to 90 % complete.
Typically the amount of oxygen that is added is such that the gas vented from the absorption zone or zones contains from 4 5 to 7 % by volume of oxygen 15 In converting an existing process to operation in accordance with the invention, it is preferred that the enrichment in oxygen of the bleaching air should be carried out so as to increase the partial pressure of the oxygen at the region of the absorption zone or zones where the bleaching air becomes mixed with the cooled gas by 10 to 20 % Furthermore, it is preferred that the reduction-in the rate at which bleaching air is taken to form the secondary 20 air is sufficient to reduce the velocity of the gas passing through the absorption zone or zones by from 5 to 18 % the said velocity being that at the location where the bleaching air units with the cooled gas In addition, it is preferred that the enrichment in oxygen of the gas passing through the absorption zone or zones is sufficient to increase by 30 to 100 % the partial pressure of oxygen in the gas at the region where the enriching gas unites with the 25 oxygen passing through the column.
Performing the process according to the present invention, makes it possible to obtain a reduction in the operating pressure of the or each operating zone In some instances, we believe, it may also be possible to reduce the number of absorption columns that are used if a plant contains two or more columns 30 In converting an existing plant to operation in accordance with the present invention it is not necessary to increase the rate at which molecular oxygen flows through the bleaching zone Thus, it is possible to avoid making a significant increase in the dissolved oxygen in the nitric acid product Any such increase in the dissolved oxygen concentration would be troublesome if the product nitric acid is produced at elevated pressure and then subjected to 35 a reduction in pressure.
The result of such a reduction in pressure would be an emission of oxygen which could be a fire hazard.
Those skilled in the art of designing plants making nitric acid will appreciate that a new plant may be custom-built for operating the process according to the invention 40 If a new plant is built to operate the method according to the present invention, analogous advantages to those described above may be achieved In addition, the process according to the present invention may offer an increased flexibility in selecting the wall-thickness of the or each absorption column, the number of trays, the number of columns, their height and diameter, size of the bleaching tower and the size of the 45 compressors.
Typically product nitric acid of from 50 to 70 % strength may be produced by the process according to the invention.
The invention will now be described by way of example with reference to the accompanying drawing which is a circuit diagram showing a plant for manufacturing nitric 50 acid.
Referring to the drawing, the illustrated plant includes a pipeline 1 for incoming air which is connected to the inlet of a compressor 3 The outlet of the compressor 3 is connected to a heat exchanger 5 The heat exchanger 5 has an outlet in communication with a pipeline 7 for cooled air The pipeline 7 terminates in a union with a pipeline 8 and a pipeline 10 The 55 pipeline 10 is in communication with the inlet of a catalytic converter or burner 17 and, upstream of the converter or burner 17, is joined by a pipe 12 through which ammonia from a source (not shown) may be introduced into the pipeline 10 and become mixed with the air before it enters the converter or burner 17.
The converter or burner 17 has an outlet for reaction or combustion products in 60 communication with a line 18 in which are disposed a first heat exchanger 19 and a second heat exchanger 22, which also functions as a condenser The condenser 22 has a first outlet in communication with a line 23 which terminates in an inlet 24 to the bottom of an absorption column 28 containing a number of sieve trays or bubble cap trays (not shown).
The condenser 22 has a second outlet in communication with a line 26 which terminates in 65 6 1,603,630 6 an inlet 29 to the column, through which inlet fluid may be introduced into the column 28 at an intermediate level thereof.
The absorption column 28 also has an inlet 42 through which water may be introduced into the top of the column; an outlet 40 through which gas may be vented from the top of the column and an inlet 30 through which oxygen or oxygen-enriched air may be introduced 5 into the column at a level above that at which fluid from the line 26 is introduced in the column but below that at which water is introduced thereto through the inlet 42.
The absorption column 28 also has an outlet line 36 in communication with an inlet 37 situated at the top of a bleaching tower 34 The bleaching tower has at its top a gas outlet in communication with a passage 38 which terminates in the pipeline 23 The bleaching tower 10 34 also has an outlet 44 for nitric acid and an inlet near its bottom in communication with a passage 8 which meets the previously-mentioned pipelines 7 and 10 in a common union.
The passage 8 has in communication with it a pipe 32 through which commercial oxygen or oxygen-enriched air may be passed into the passage 8 from a source (not shown).
In operation of the plant air may be passed through the compressor 3 where it is 15 compressed from atmospheric pressure to a chosen pressure in the range from just greater than one bar to twelve bars The air is then cooled in heat exchanger 5 Part of the air is then passed via line 8 into the bleaching tower 34 The majority, however, passes into the line 10 and becomes mixed with ammonia introduced via line 12 This mixture passes via line 10 into the converter 17 where the ammonia is burned to form nitric oxide 20 The combustion products consisting mainly of nitric oxide, nitrogen, water vapour and oxygen leave the burner 17 via line 18 and then pass through the heat exchanger 19 and the condenser 22 The outlet temperature of the gas leaving the condenser 22 is in the order of 40-800 C.
In the condenser 22 some of the nitric oxide will react with oxygen in the gas mixture 25 therewith to form nitrogen dioxide Nitrogen dioxide then undergoes a dimerisation reaction to form dinitrogen tetroxide The nitrogen dioxide and dinitrogen tetroxide react with water vapour condensed in the condenser so as to form dilute nitric acid The dilute nitric acid is introduced into the absorption column 28 through the inlet 29.
Uncondensed gases leaving the condenser 22 enter the bottom of the absorption column 30 28 through the inlet 24 These gases pass upwardly through the trays in the column 28 and contact water descending the column, the water having been introduced through the inlet 42 Before entering the column through the inlet 24 the uncondensed gases from the condenser 22 are joined by vent gases leaving the bleaching tower 34 via the passage 38.
In the column, dinitrogen tetroxide and nitrogen dioxide react with water to form nitric 35 acid and nitric oxide The nitric oxide reacts with oxygen to form nitrogen dioxide which dimerises The dinitrogen tetroxide so formed reacts with the water to form more nitric acids, and nitric oxide, and so on Oxygen or oxygen-enriched air is introduced into the column 28 via the inlet 30 The oxygen so-introduced helps to promote conversion of nitric oxide to nitrogen dioxide and its dimer The inlet 30 is situated at a level such that the 40 oxygen or oxygen-enriched air enters the column and unites with the gas passing through the column at a location where the absorption reaction is from to 70 to 90 % complete.
Unabsorbed gas is vented from the column through the line 40 Nitric acid collected at the bottom of the column is passed into the top of the bleaching tower where it is contacted with air introduced into the column via the passage 8 This air is enriched in oxygen by the 45 addition of oxygen through the line 32 The action of the oxygen-enriched air introduced into the bleaching tower 34 is to oxidise impurities in the nitric acid and also to strip from the nitric acid any dissolved oxides of nitrogen The oxygen-enriched air is then taken as secondary air and united with the cooled nitric oxide containing gas mixture as it enters the absorption column Nitric acid product is taken from the bleaching column 34 via the line 50 44. Typically, the vent gas leaving the plant through the line 40 will
consist mainly of nitrogen, with small quantities of oxygen and 1500 ppm or less of oxides of nitrogen, depending on the pressure at which the absorption column is operated.
The invention is further illustrated by the following example: 55 Example
This example relates to the uprating of a standard plant (such as that illustrated in the accompanying drawing) for making nitric acid The plant when operated conventionally is intended to produce 14 8 tonnes/hr of nitric acid in a 60 % solution 60 In conventional operation 5 440 m 3/hr of air are mixed at a pressure of 5 bar and passed to the ammonia burner Ammonia is passed into the burner at a rate sufficient to form a gas comprising 10 4 % by volume of nitric oxide, 5 0 % by volume of oxygen, 16 0 % by volume of water vapour, and the remainder nitrogen.
The gas mixture is then cooled in a waste heat boiler and then two coolercondensers 65 7 1,603,630 7 where dilute nitric acid is formed at a concentration of 55 % by weight The remainder of the gases are mixed with secondary air to form a gas mixture comprising by volume 2 8 % of nitric oxide, 5 8 % of nitrogen dioxide (molecules of dinitrogen tetroxide are treated as two molecules of nitrogen dioxide), 5 7 % of oxygen, and 0 6 % of water, the remainder being nitrogen The gas mixture is introduced into the bottom of an absorption column The gas 5 velocity at the bottom of the column is 0 15 metres per second It becomes progressively smaller as the reaction proceeds in the column The unabsorbed gases leaving the absorber have the following composition oxides of nitrogen 1500 ppm, 2 85 % by volume of oxygen, and the remainder being nitrogen.
The product nitric acid is passed into a bleaching column where compressed air is passed 10 through the acid at a fifth of the rate at which it enters the burner The gas leaving the bleaching column is taken to form the secondary air.
The plant is uprated by 10 % so that 16 3 tonnes per hour of nitric acid dissolved in sufficient water to produce 60 % acid are formed The rate at which bleaching air is passed into the bleaching column is reduced by 45 % by volume and the extra compressed air thus 15 produced is passed into the burner In addition the rate of flow of ammonia into the burner is increased by 10 % so that the relative proportions of the air and ammonia entering the burner remain unaltered.
Pure oxygen is added to the bleach air such that the quantity of oxygen flowing through the bleaching column is unaltered Thus, a bleaching gas comprising oxygenenriched air 20 containing 33 % by volume of oxygen, and 67 % by volume of nitrogen is formed This results in a total reduction of 36 % in the rate of flow of gas through the bleaching column.
In addition, there is a corresponding reduction in the rate of flow of secondary air into the absorption column This leads to a reduction in the gas velocity at the bottom of the column, the reduced velocity being 0 13 m/sec As, however, the total flow rate of oxygen 25 into the absorption column is unaltered, it is necessary to add extra oxygen so as to prevent the concentration of oxides of nitrogen in the vent gas from increasing Oxygen (substantially pure) is added to the column at a region where the absorption reaction is from to 90 % complete Typically, in a column containing about 30 trays, this may be above the 8th tray from the bottom The rate of adding oxygen is sufficient above this tray to 30 increase the oxygen in the vent gas to 4 5 to 7 % by volume Thus the total oxygen added (both to the bleaching air and to the gas passing through the absorption column) amounts to 0.85 tonne for each extra tonne of nitric acid produced.
Claims (1)
WHAT WE CLAIM IS:-
1 A gas-liquid contact process for making nitric acid including the steps of: 35 (a) reacting primary air and ammonia catalytically at elevated temperature to form a gas comprising nitric oxide, nitrogen, oxygen and water vapour; (b) cooling the gas to a temperature at which water vapour condenses; {c) introducing the cooled gas into one or more columnar absorption zones and contacting it countercurrently with water and thereby forming product nitric acid; 40 (d) passing the product nitric acid into a bleaching zone wherein bleaching air is passed through the product nitric acid; (e) enriching the bleaching air in oxygen, in, upstream of, or downstream of, the bleaching zone; (f) passing secondary air through the or each absorption zone with the cooled gas, the 45 secondary air being constituted at least in part by the oxygen-enriched bleaching air; (g) enriching in oxygen the gas passing through the absorption zone(s) at one or more regions where the absorption reaction is from 50 to 90 % complete.
2 A process as claimed in claim 1, in which the secondary air is constituted entirely by oxygen-enriched air which has passed through the said bleaching zone 50 3 A process as claimed in claim 1, in which air from the atmosphere is added to oxygen-enriched air which has passed through the bleaching zone so as to form the secondary Fir.
4 A process as claimed in claim 1, in which the oxygen-enriched bleaching air contains 25 to 45 % by volume of oxygen 55 A process as claimed in claim 4, in which the ratio:
AB + AF AB + AE + Ap 60 expressed as a percentage is the range 5 to 12 %, wherein:
AB represents the rate (mass per unit time) at which air is taken to form the bleaching air; AE represents the rate (mass per unit time) at which air is added to the bleaching air to form the secondary air, and Ap represents the rate (mass per unit time) at which the primary air enters the catalytic 65 1,603,630 reaction zone(s).
6 A process as claimed in claim 5, in which the ratio is in the range 5 to 8 %.
7 A process as claimed in claim 5 or claim 6, in which AE = 0.
8 A process as claimed in any one of the preceding claims, in which the bleaching zone is situated in a column which defines the absorption zone or one of the absorption zones 5 9 A process as claimed in any one of claims 1 to 7, in which the bleaching zone is situated within a column separate from the absorption column or columns.
A process as claimed in any one of the preceding claims, in which commercial oxygen (as hereinbefore defined) is used to enrich in oxygen the gas passing through the absorption zone or zones, the commercial oxygen being introduced into the absorption 10 zone or zones at a rate in the range 2 to 15 % of that at which the cooled gas enters the absorption zone or zones.
11 A process as claimed in any one of the preceding claims, in which the gas passing through the absorption zone or zones is enriched in oxygen at one or more regions where the absorption reaction is from 70 to 90 % complete 15 12 A process as claimed in any one of the preceding claims, in which the gas vented from the absorption zone or zones contains from 4 5 to 7 % by volume of oxygen.
13 A method of improving a process for making nitric acid, the process including the steps of:
(a) reacting primary air and ammonia catalytically at elevated temperature to form a 20 gas comprising nitric oxide, nitrogen, oxygen and water vapour; (b) cooling the gas to a temperature at which water vapour condenses; (c) introducing the cooled gas into one or more columnar absorption zones and contacting it countercurrently with water and thereby forming product nitric acid; (d) passing the produce nitric acid into a bleaching zone wherein bleaching air is passed 25 through the product nitric acid; (e) passing secondary air through the or each absorption zone with the cooled gas, the secondary air being constituted at least in part by bleaching air taken from the bleaching zone; the improvement being effected by: 30 1 making a reduction in the rate at which the bleaching air or any other air is taken to form the secondary air; 2 enriching the bleaching air in oxygen upstream of, in or downstream of the bleaching zone; 3 enriching in oxygen the gas passing the absorption zone or zones at one or more 35 regions where the absorption reaction is from 50 to 90 % complete; and thereby performing a process as claimed in claim 1.
14 A method as claimed in claim 13, in which an increase is made in the rate at which, primary air and ammonia are introduced into the catalytic reaction zone(s) so as to produce an increase in the rate of production of product nitric acid without increasing the 40 concentration of nitric oxides in gas vented from the absorption zone or zones.
A method as claimed in claim 13, in which a decrease is made in the rate at which water is introduced into the absorption zone or zones, and a product acid of increased concentration is produced without there being an increase in the concentration of oxides of nitrogen in gas vented from the absorption zone or zones 45 16 A method as claimed in any one of claims 13 to 15, in which the enrichment in oxygen of the bleaching air increases the partial pressure of the oxygen at the region of the absorption zone or zones where the bleaching air becomes mixed with the cooled gas by 10 to 20 %.
17 A method as claimed in any one of claims 13 to 16, in which the reduction in the rate 50 at which bleaching air is taken to form the secondary air is sufficient to reduce the velocity of the gas passing through the absorption zone or zones by from 5 to 18 %, the said velocity being that at the location where the bleaching air unites with the cooled gas.
18 A method as claimed in any one of claims 13 to 17 in which the enrichment in oxygen of the gas passing through the absorption zone or zones is sufficient to increase by 55 to 100 % the partial pressure of oxygen in the gas at the region where the enriching gas unites with the oxygen passing through the column.
19 A method as claimed in any one of claims 13 to 18, in which the bleaching air is enriched upstream of the bleaching zone.
20 A method as claimed in any one of claim 19, in which the secondary air is 60 constituted entirely by the oxygen-enriched bleaching air.
21 A method as claimed in any one of claims 13 to 20, in which the bleaching air after enrichment in oxygen contains from 25 to 45 % by volume of oxygen.
22 A method as claimed in claim 21 in which after the rate at which the bleaching air is taken to form the secondary air is reduced, the ratio 65 AR + AE AB + AE + Ap expressed as a percentage is in the range 5 to 12 %, wherein:
AB represents the rate (mass per unit time) at which air is taken to form the bleaching air; 5 AE represents the rate (mass per unit time) at which air is added to the oxygen-enriched bleaching air to form the secondary air, and Ap represents the rate (mass per unit time) at which the primary air enters the catalytic reaction zone(s).
23 A method as claimed in claim 22, in which the ratio is in the range 5 to 8 % 10 24 A method as claimed in claim 22 or claim 23, in which AE= 0.
A method as claimed in any one of claims 13 to 24, in which the bleaching zone is situated in a column which defines the absorption zone or one of the absorption zones.
26 A method as claimed in any one of claims 13 to 24, in which the bleaching zone is situated within a column separate from the absorption column or columns 15 27 A method as claimed in any one of claims 13 to 26, in which the gas passing through the absorption zone or zones is enriched in oxygen at one or more regions where the absorption reaction is from 70 to 90 % complete.
28 A method as claimed in any one of the preceding claims, in which the gas vented from the absorption zone or zones contains from 4 5 to 7 % (by volume or by weight) of 20 oxygen.
29 A gas-liquid contact process for making nitric acid, substantially as herein described herein with reference to the accompanying drawing.
A gas-liquid contact process for making nitric acid, substantially as described herein in the Example 25 For the Applicant M WICKHAM Chartered Patent Agent Printed for Her Majesty's Stationery Office by Croydon Printing Company Limited, Croydon, Surrey 1981.
Published by The Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained.
GB25269/77A
1977-06-16
1977-06-16
Gas-liquid contact process
Expired
GB1603630A
(en)
Priority Applications (10)
Application Number
Priority Date
Filing Date
Title
GB25269/77A
GB1603630A
(en)
1977-06-16
1977-06-16
Gas-liquid contact process
IE1207/78A
IE47094B1
(en)
1977-06-16
1978-06-15
Gas liquid contact process
IT24595/78A
IT1096666B
(en)
1977-06-16
1978-06-15
CONTACT PROCESS BETWEEN GAS AND LIQUID ESPECIALLY FOR THE PRODUCTION OF NITRIC ACID
ES470814A
ES470814A1
(en)
1977-06-16
1978-06-15
Oxygen-enrichment columnar absorption process for making nitric acid
FR7817952A
FR2394493A1
(en)
1977-06-16
1978-06-15
PERFECTED PROCESS FOR MANUFACTURING NITRIC ACID BY GAS-LIQUID CONTACT
US05/915,861
US4183906A
(en)
1977-06-16
1978-06-15
Oxygen-enrichment columnar absorption process for making nitric acid
DE19782826143
DE2826143A1
(en)
1977-06-16
1978-06-15
PROCESS FOR THE PRODUCTION OF NITRIC ACID
AU37181/78A
AU517218B2
(en)
1977-06-16
1978-06-16
Preparation of nitric acid
NLAANVRAGE7806528,A
NL188033C
(en)
1977-06-16
1978-06-16
METHOD FOR PREPARING SALPIC ACID.
BE188643A
BE868207A
(en)
1977-06-16
1978-06-16
NITRIC ACID PRODUCTION PROCESS
Applications Claiming Priority (1)
Application Number
Priority Date
Filing Date
Title
GB25269/77A
GB1603630A
(en)
1977-06-16
1977-06-16
Gas-liquid contact process
Publications (1)
Publication Number
Publication Date
GB1603630A
true
GB1603630A
(en)
1981-11-25
Family
ID=10224975
Family Applications (1)
Application Number
Title
Priority Date
Filing Date
GB25269/77A
Expired
GB1603630A
(en)
1977-06-16
1977-06-16
Gas-liquid contact process
Country Status (10)
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US
(1)
US4183906A
(en)
AU
(1)
AU517218B2
(en)
BE
(1)
BE868207A
(en)
DE
(1)
DE2826143A1
(en)
ES
(1)
ES470814A1
(en)
FR
(1)
FR2394493A1
(en)
GB
(1)
GB1603630A
(en)
IE
(1)
IE47094B1
(en)
IT
(1)
IT1096666B
(en)
NL
(1)
NL188033C
(en)
Families Citing this family (14)
* Cited by examiner, † Cited by third party
Publication number
Priority date
Publication date
Assignee
Title
DE2850054A1
(en)
*
1978-11-14
1980-05-29
Uhde Gmbh
METHOD FOR PRODUCING Nitric Acid
DE2939674A1
(en)
*
1979-09-29
1981-04-09
Hoechst Ag, 6000 Frankfurt
METHOD FOR ABSORPING NITROSE GASES
EP0297738B1
(en)
*
1987-06-29
1992-03-25
United Kingdom Atomic Energy Authority
A method for the treatment of waste matter
US4869890A
(en)
*
1988-04-05
1989-09-26
Air Products And Chemicals, Inc.
Control of nitric acid plant stack opacity during start-up and shutdown
US5167935A
(en)
*
1989-01-26
1992-12-01
Beco Engineering Company
Apparatus for treatment of nitrogen oxides
ID16932A
(en)
*
1996-05-23
1997-11-20
Praxair Technology Inc
DIRECT OXYGEN SPRAYER IN NITRATE ACID PRODUCTION
US5985230A
(en)
*
1996-10-03
1999-11-16
L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Nitric acid production
US6165435A
(en)
*
1998-12-24
2000-12-26
Praxair Technology, Inc.
Method and production of nitric acid
US6333411B1
(en)
1998-12-24
2001-12-25
Praxair Technology, Inc.
Method for production of hydroxylammonium phosphate in the synthesis of caprolactam
US6469163B1
(en)
1998-12-24
2002-10-22
Praxair Technology Inc.
Method for production of hydroxylamine sulfate in the conventional process for the synthesis of caprolactam
DE102013002201A1
(en)
*
2013-02-07
2014-08-07
Messer Austria Gmbh
Process and production plant for the production of nitric acid
DE102013004341A1
(en)
2013-03-14
2014-09-18
Thyssenkrupp Uhde Gmbh
Process for the oxidation of ammonia and suitable plant
EP3372556A1
(en)
2017-03-07
2018-09-12
Casale Sa
A plant for the production of nitric acid, a related process and method of revamping
EP4015451A1
(en)
*
2020-12-17
2022-06-22
Yara International ASA
Mono-pressure plant for the production of nitric acid and method for operating same
Family Cites Families (13)
* Cited by examiner, † Cited by third party
Publication number
Priority date
Publication date
Assignee
Title
US1338417A
(en)
*
1918-09-30
1920-04-27
Norsk Hydro Elektrisk
Manufacture of concentrated nitric acid
NL26884C
(en)
*
1929-02-27
US2046162A
(en)
*
1934-02-20
1936-06-30
Du Pont
Process for producing concentrated nitric acid
GB758417A
(en)
*
1953-08-21
1956-10-03
Manuf De Prod Chim Du Nord Ets
A process of manufacture of nitric acid
BE551022A
(en)
*
1955-09-14
1900-01-01
GB910131A
(en)
*
1957-08-26
1962-11-07
Secr Aviation
Improvements in or relating to processes for increasing the concentration of nitric acid
US3081153A
(en)
*
1959-03-13
1963-03-12
Phillips Petroleum Co
Automatic optimum air addition to nitric oxide absorption in nitric acid production
GB1051100A
(en)
*
1963-08-15
1900-01-01
NL6401801A
(en)
*
1964-02-25
1965-08-26
US3464788A
(en)
*
1965-12-15
1969-09-02
Foster Wheeler Corp
Process and apparatus for production of nitric acid
AT270684B
(en)
*
1966-11-15
1969-05-12
Belge Produits Chimiques Sa
Process for the production of concentrated nitric acid
GB1306581A
(en)
*
1969-02-28
1973-02-14
Pintsch Bamag Ag
Process for the production of nitric acid with a concentration of over 70percent by weight
US3927182A
(en)
*
1971-02-25
1975-12-16
James Basil Powell
Process for making nitric acid by the ammonia oxidation-nitric oxide oxidation-water absorption method
1977
1977-06-16
GB
GB25269/77A
patent/GB1603630A/en
not_active
Expired
1978
1978-06-15
DE
DE19782826143
patent/DE2826143A1/en
not_active
Withdrawn
1978-06-15
ES
ES470814A
patent/ES470814A1/en
not_active
Expired
1978-06-15
US
US05/915,861
patent/US4183906A/en
not_active
Expired - Lifetime
1978-06-15
IT
IT24595/78A
patent/IT1096666B/en
active
1978-06-15
FR
FR7817952A
patent/FR2394493A1/en
active
Granted
1978-06-15
IE
IE1207/78A
patent/IE47094B1/en
unknown
1978-06-16
NL
NLAANVRAGE7806528,A
patent/NL188033C/en
not_active
IP Right Cessation
1978-06-16
BE
BE188643A
patent/BE868207A/en
unknown
1978-06-16
AU
AU37181/78A
patent/AU517218B2/en
not_active
Expired
Also Published As
Publication number
Publication date
FR2394493B1
(en)
1983-02-25
ES470814A1
(en)
1980-01-01
IE781207L
(en)
1978-12-16
AU3718178A
(en)
1979-12-20
IE47094B1
(en)
1983-12-14
FR2394493A1
(en)
1979-01-12
US4183906A
(en)
1980-01-15
BE868207A
(en)
1978-12-18
IT1096666B
(en)
1985-08-26
AU517218B2
(en)
1981-07-16
DE2826143A1
(en)
1978-12-21
NL188033B
(en)
1991-10-16
IT7824595D0
(en)
1978-06-15
NL188033C
(en)
1992-03-16
NL7806528A
(en)
1978-12-19
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Legal Events
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Code
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Description
1982-02-17
PS
Patent sealed [section 19, patents act 1949]
1998-06-24
PE20
Patent expired after termination of 20 years
Effective date:
19980530
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