EP0655986A1 - Procede et appareil de neutralisation d'ecoulement d'acide - Google Patents

Procede et appareil de neutralisation d'ecoulement d'acide

Info

Publication number
EP0655986A1
EP0655986A1 EP93918055A EP93918055A EP0655986A1 EP 0655986 A1 EP0655986 A1 EP 0655986A1 EP 93918055 A EP93918055 A EP 93918055A EP 93918055 A EP93918055 A EP 93918055A EP 0655986 A1 EP0655986 A1 EP 0655986A1
Authority
EP
European Patent Office
Prior art keywords
reaction zone
calcium hydroxide
solution
acid stream
neutralisation
Prior art date
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.)
Withdrawn
Application number
EP93918055A
Other languages
German (de)
English (en)
Inventor
Stephen Patrick Kieran 29 Limesford Road Walsh
David Hugh Annells
John Joseph Harkin
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.)
Imperial Chemical Industries Ltd
Original Assignee
Imperial Chemical Industries 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.)
Filing date
Publication date
Application filed by Imperial Chemical Industries Ltd filed Critical Imperial Chemical Industries Ltd
Publication of EP0655986A1 publication Critical patent/EP0655986A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • A—HUMAN NECESSITIES
    • A62—LIFE-SAVING; FIRE-FIGHTING
    • A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
    • A62D3/00—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances
    • A62D3/30—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances by reacting with chemical agents
    • A62D3/36—Detoxification by using acid or alkaline reagents
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
    • A—HUMAN NECESSITIES
    • A62—LIFE-SAVING; FIRE-FIGHTING
    • A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
    • A62D2101/00—Harmful chemical substances made harmless, or less harmful, by effecting chemical change
    • A62D2101/40—Inorganic substances

Definitions

  • This invention relates to a process for the neutralisation of aqueous acid streams with calcium hydroxide, and in particular to a process of neutralising a hydrochloric acid stream with calcium hydroxide.
  • the invention relates in a further aspect to an apparatus in which the process of the invention may be effected.
  • Hydrochloric acid is produced on a wide scale around the world, indeed it is produced as a by-product in very many industrial processes. In particular it is produced as a by-product in the reaction of chlorine containing compounds with hydrogen fluoride in which fluorine is exchanged for chlorine, many of which are practised around the world.
  • hydrochloric acid may be a commercial product in itself, it is not practical to store large quantities for lengthy periods of time and consequently, if an immediate demand cannot be found, then it is necessary to dispose of the hydrochloric acid. Disposal of the acid involves first neutralising the acid stream followed by discharge of the neutralised effluent.
  • sodium hydroxide is convenient to use due to its high solubility in water which allows it to be employed in the form of an aqueous solution, it is significantly more expensive than calcium hydroxide and poses problems of both pH measurement, due to the presence of sodium ions which have a deleterious effect on the operation of pH meters, and control, due to the characteristic titration curve which shows a very sharp change in pH over a very small change in sodium hydroxide addition in the neutral region.
  • the use of calcium (hydr)oxide has posed various problems associated with the low degree of solubility of calcium hydroxide in water such that calcium hydroxide is predominantly present in solid form when added to the acid stream. In particular it poses control problems in ensuring that the calcium hydroxide has sufficiently reacted with the acid so that downstream carryover of solid reagent and subsequent reaction does not cause pH increase after the neutralisation process.
  • the process of the present invention is based upon the use of calcium hydroxide as the neutralising agent.
  • CSTR continuous stirred tank reactor vessels
  • a process for the neutralisation of an acid stream which process comprises feeding the acid stream and calcium hydroxide through a first reaction zone to a second reaction zone so that the calcium hydroxide partially neutralises the acid stream during feed of the stream to the second reaction zone, the second reaction zone being provided with means for measuring the pH of the solution within the second reaction zone and means for feeding aqueous base to the second reaction zone.
  • the first reaction zone may comprise a conduit to which the acid stream and a calcium hydroxide stream are fed, and the acid and calcium hydroxide streams may be combined to flow through the conduit co-currently to the second reaction zone.
  • the acid streams which are neutralised by the process of the invention need not be diluted prior to neutralisation and the acid streams will usually therefore be concentrated streams, for example acid streams with an acid concentration of at least 102 by weight, and especially acid concentrations of at least 252 by weight. Acid streams having a concentration of up to 352 or 402 by weight may be neutralised with satisfactory control by the process of the invention.
  • the acid stream is preferably that of an acid, the calcium salt of which is soluble in aqueous solution.
  • the acid stream will usually be a hydrochloric acid or nitric acid stream, although small amounts of other acids, for example sulphuric and hydrofluoric acid may also be present.
  • the calcium hydroxide fed to the first reaction zone is preferably in the form of an aqueous slurry of calcium hydroxide.
  • the aqueous slurry of calcium hydroxide is preferably prepared from powdered hydrated lime in order to reduce the amount of heat liberated during the slurrying process and thus the temperature of the reagent.
  • the proportion of solids in the slurry may vary within a wide range but preferably the calcium hydroxide slurry contains from about 102 solids by weight to about 402 solids by weight, especially from about 152 by weight to about 252 by weight.
  • the calcium hydroxide component of the slurry preferably comprises calcium hydroxide solids particles with a mean particle size in the range from about 1 micron to about 10 micron with less than about 0.12 of the particles having a size larger than about 250 microns, in order to promote rapid reaction of the calcium hydroxide with the acid.
  • the first reaction zone comprises a Plug Flow reactor.
  • the second reaction zone is preferably a Stirred Tank Reactor.
  • Plug Flow and Stirred Tank Reactors are conventional within the art and any design of these reactors may be employed in the process of the invention.
  • the reactors are preferably constructed of materials resistant to the chemical streams with which they are to be contacted.
  • the reactors may be constructed using rubber, per-fluorinated copolymers, for example polytetrafluoroethylene , or from metal alloy systems also having resistance to the chemical streams within them, for example suitable Hastelloy or Inconel alloys.
  • the reactors may also comprise for example steel, having an inner lining of these materials. In practice we prefer to use rubber coated carbon steel.
  • a first reaction zone comprising a plug flow reactor which serves to maximise the extent of reaction for any given reactor volume, allows the most efficient reaction of the calcium hydroxide and thus reduces the reactor volume required for sufficient conversions of the calcium hydroxide thus reducing the tendency for any carry-over of unreacted calcium hydroxide from the neutralisation process.
  • the accelerated reaction of calcium hydroxide which we have found under acid conditions is further enhanced by the use of the plug flow reactor.
  • the plug flow reactor employed in the process preferably comprises a static mixer into which the acid and calcium hydroxide streams are fed followed by a length of pipe sufficient to allow adequate reaction of the calcium hydroxide.
  • the optimum capacity of the plug flow reaction zone depends upon the properties of the acid stream and of the calcium hydroxide, in particular the particle size distribution of the calcium hydroxide reagent.
  • may commercially available forms of calcium hydroxide may contain calcium carbonate impurities which may yield carbon dioxide during the process. The presence of such carbon dioxide may also influence the desired capacity of the plug flow reactor.
  • sufficient length of plug flow reactor to allow a residence time within the reaction zone of at least 30 seconds, preferably at least 35 seconds and especially at least 40 seconds.
  • the acid stream and calcium hydroxide are fed to the first reactor zone under ratio feed-forward control in order to control the degree of neutralisation which is effected in the first reaction zone.
  • Ratio feed forward control of the streams may be achieved by monitoring, for example, the density or conductivity of the acid stream whereby to obtain the acid concentration of the acid stream and by monitoring the flow of the stream.
  • the flow of calcium hydroxide slurry theoretically required to achieve a required first degree of neutralisation (as described hereinafter) in the first reaction zone may then be calculated and that flow of calcium hydroxide may be fed to the first reaction zone.
  • the required degree of neutralisation in the first reaction zone may vary within a wide range but preferably sufficient calcium hydroxide is fed to the first reaction zone to effect as large a proportion of the total neutralisation as possible, thus reducing to a minimum the amount of further aqueous base required to be added to the second reaction zone whilst allowing a substantial acid concentration to be maintained throughout the first reaction zone and minimising the chance of carry-over of calcium hydroxide and hence pH overshoot following the neutralisation.
  • the amount of calcium hydroxide fed to the first reaction zone is sufficient to effect at least 802 of the neutralisation, more preferably at least 902, and especially about 952 of the neutralisation.
  • the ratio of the flow of calcium hydroxide slurry and acid to the first reaction zone is also adjusted by a feedback control loop from the proportion of aqueous base added to the second reaction zone whereby to compensate any variations in the concentration of the calcium hydroxide feed to the first reaction zone and so as to maintain the desired proportion of calcium hydroxide being added to the first reaction zone.
  • the product of the first reaction zone is then fed to a second reaction zone which comprises a Stirred Tank Reactor, preferably a Continuous Stirred Tank Reactor (CSTR), to which further aqueous base is added, preferably under feedback control from means for monitoring the pH of the solution within the CSTR, in an amount sufficient to achieve a second required degree of neutralisation.
  • CSTR Continuous Stirred Tank Reactor
  • the amount of aqueous base necessary to achieve the required second degree of neutralisation will depend upon the amount of calcium hydroxide fed to the first reaction zone, but in order that a reliable reading may be taken from the pH meter, the amount of aqueous base added is preferably such as to result in a solution which may be recovered from the second reaction zone having a pH of at least 1, preferably at least 1.5.
  • the amount of aqueous base added may be such as to produce a solution having a pH of not greater than 4, preferably not greater than 3.
  • the aqueous base which is added to the second reaction zone is preferably calcium hydroxide since the use of calcium hydroxide in the second reaction zone as well as the first reaction zone promotes the buffering effect previously described.
  • other aqueous bases may be employed if desired, for example sodium hydroxide.
  • a process for the neutralisation of an acid stream which comprises the steps of (a) feeding to a first reaction zone under ratio-feed-forward control the acid stream to be neutralised and sufficient calcium hydroxide whereby to perform a first required degree of neutralisation (as hereinbefore described), wherein said first reaction zone comprises a plug flow reactor, (b) feeding the product from step (a) to a second reaction zone comprising a stirred tank reactor provided with means for measuring the pH of the solution within the tank and feeding calcium hydroxide thereto, wherein a feedback control loop from the pH measuring means controls the addition of sufficient calcium hydroxide to the tank to perform a second required degree of neutralisation and (c) recovering a solution from the second reaction zone having a pH of from about 1 to about 3.
  • the solution recovered from step (c) may then be passed to a third reaction zone in which fine adjustment of the solution to a pH of between 6 and 9 is carried out by the addition of small amounts of an aqueous base under feedback control.
  • the aqueous base employed may be calcium hydroxide, or it may be another aqueous base, for example sodium hydroxide.
  • achieving the required pH control in the third reaction zone in order to meet discharge requirements is facilitated by a strong buffering effect (reduced sensitivity of pH to concentration variations) observed when employing calcium hydroxide as the neutralisation reagent in the first reaction zone in which the major part of the neutralisation is effected, and preferably also as the aqueous base which is added to the second reaction zone.
  • This buffering effect may be exploited in the third reaction zone by the use of calcium or sodium hydroxide.
  • the pH in the third reaction zone is preferably controlled to a value we have determined by investigation of the chemical characteristics of the calcium hydroxide/acid system, to give a pH on solids removal and cooling which is within the regulatory pH limits allowed for effluent discharge. Consequently, cooling may be carried out ' on the final neutralised stream without the need for subsequent pH adjustment on the cooled stream.
  • Cooling may be carried out, for example by evaporative cooling.
  • the pH sensing means employed in the third reaction zone is pre-set to compensate for the effect of the temperature reduction (cooling) on the pH .
  • the pH of the pre-cooled solution may therefore be from about 6.5 to about 7.5, such that after cooling, the neutralised stream to be discharged has a pH within the range from about 7.5 to about 8.5.
  • an apparatus for the neutralisation of an acid stream with calcium hydroxide which comprises a first plug flow reaction zone provided with means for feeding the acid stream and calcium hydroxide thereto under ratio feed-forward control, and a second reaction zone comprising a continuous stirred tank reactor provided with means for measuring the pH of the solution therein, an aqueous base feed and feedback control means for controlling the addition of aqueous base thereto.
  • the invention is illustrated but not limited by the following figure which is a schematic flow diagram of an apparatus in which the process of the invention may be operated.
  • a plug flow reactor 1 comprises a static mixer 2 and a pipeline 3 constructed from rubber-lined carbon steel.
  • a hydrochloric acid feed line 4 to the static mixer 2 is provided with a conductivity meter 5 and flow meter 6. The outlets from the conductivity and flow meters are connected to a ratio feed-forward control unit 7.
  • a calcium hydroxide feed line 8 to the static mixer 2 is provided with flow meter 9 and valve 10. Flow meter 9 and valve 10 are connected to the outlet from the ratio feed-forward control unit 7. Outlet 11 from the pipeline 3 enters a
  • Continuous Stirred Tank Reactor (CSTR) 12 which is provided with an agitator 13, pH meter 14 and calcium hydroxide feed line 15.
  • Calcium hydroxide feed line 15 is provided with a valve 16 controlled by feedback circuitry 17 connected to the pH meter 14.
  • Outlet 18 from the CSTR 12 is connected to inlet 19 of a Continuous Stirred Tank Reactor (CSTR) 20 which is provided with an agitator 21, pH meter 22 and sodium hydroxide feed line 23.
  • Sodium hydroxide feed line 23 is provided with a valve 24 controlled by feedback circuitry 25 connected to the pH meter 22.
  • Outlet 26 from the CSTR 20 is connected to downstream cooling and solids removal equipment (not shown).
  • the hydrochloric acid feed stream is fed through line 4, conductivity meter 5 and flow meter 6 to the static mixer 2.
  • the conductivity and flow measurements are fed to the ratio feed-forward control unit 7 which performs a mathematical ratio function based on the theoretically required amount of calcium hydroxide required to neutralise an acid stream having the measured flow and concentration and controls the valve 10 and flow meter 9 to provide a flow of calcium hydroxide through line 8 to the static mixer 2 which is sufficient to provide 952 of the theoretical amount of calcium hydroxide required to perform the neutralisation.
  • the calcium hydroxide and hydrochloric acid streams are mixed in the static mixer 2 and flow through the pipeline 3 which is of sufficient capacity to allow a 40 second residence time within the pipe.
  • the mixed stream then enters the CSTR 12 where it is mixed by agitator 13.
  • the pH of the solution within the CSTR is continuously monitored by pH meter 14 and the addition of calcium hydroxide to the CSTR is controlled by feedback circuitry 17 from pH meter 14 to valve 16, to produce a solution in the CSTR with a pH of about 2.
  • the solution flows under gravity from outlet 18 of CSTR 12 through inlet 19 of, and into CSTR 20.
  • the pH of the solution in the CSTR 20 is then adjusted to pH 7.5 by the addition of sodium hydroxide through line 23 under the control of feedback circuitry 25 provided from pH meter 22 to valve 24 on the sodium hydroxide feed line 23.
  • the neutralised stream from outlet 26 then passes to downstream processes in which residual solids are removed and the stream is cooled, with a consequent increase in pH to about pH 8.
  • the invention is further illustrated by the following example which was conducted on a laboratory apparatus described below.
  • the apparatus comprised a 6" spiral helix plastic mixer (supplied by RS Components Ltd, Ref: 503/385) set inside a glass tubing of length 15cm and diameter 10mm, and provided with hydrochloric acid and calcium hydroxide feed inlets, each having a peristaltic pump.
  • a two metre length of rubber tubing was attached in fluid flow communication with the exit from the glass tubing, the glass and rubber tubing together providing the plug flow reaction zone and the rubber tubing having provided therein a vent for carbon dioxide generated during the neutralisation reaction.
  • a stirred tank of capacity 3.5 litres provided with a pH feedback control system comprising a pH meter set at pH 2 and a calcium hydroxide feed line.
  • the pH control system controls the feed of calcium hydroxide to this stirred tank to achieve a measured pH of 2 for the solution in the tank.
  • the outlet from the tank is connected to a second stirred tank of capacity 3.25 litres and provided with a sodium hydroxide feed line and pH feedback control system set at pH 6.1.
  • the pH control system controls the feed of sodium hydroxide to this stirred tank to achieve a measured pH of 6.1 for the solution in the tank.
  • the outlet from this second stirred tank is connected to a third vessel provided with a pH meter and in which the pH of the product neutralised solution is measured.
  • the process stream flowed continuously into the 50ml vessel in which the pH of the solution therein was measured in order to control the flow rate of the calcium hydroxide to the glass tubing to achieve a pH of 1 for the solution in this vessel.
  • the overflow from the vessel flowed into the first stirred tank beneath the vessel and in which the solution had a residence time of 15 minutes and to which further (about l.lkg/hour) calcium hydroxide was added under feedback control from the pH meter in order to achieve a measured pH for the solution exiting the tank of pH 2.
  • the solution exiting the first tank flowed continuously into the second stirred tank in which the solution had a residence time of 15 minutes and to which sodium hydroxide was added under feedback control from the pH meter in order to achieve a measured pH for the solution exiting the tank of pH 6.1.
  • the solution exiting the second stirred tank flowed into a third tank in which the pH of the product neutralised stream was measured.
  • a concentrated acid stream may be neutralised without first diluting the stream, thus directly reducing the required reactor volume and associated reactor costs, whilst providing the required control to meet the increasingly stringent requirements of environmental legislation on the pH control permitted for the neutralised discharge.
  • the rate of reaction of calcium hydroxide in the aqueous solution is in fact promoted by acid conditions and this effect may be exploited to further decrease the required reactor volumes and costs.
  • significant advantage is obtained by a buffering effect which allows effective and reliable control of pH to neutrality.

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  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Emergency Management (AREA)
  • General Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Hydrology & Water Resources (AREA)
  • Business, Economics & Management (AREA)
  • Toxicology (AREA)
  • Health & Medical Sciences (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
  • Water Supply & Treatment (AREA)
  • Organic Chemistry (AREA)
  • Physical Or Chemical Processes And Apparatus (AREA)
  • Paper (AREA)
  • Removal Of Specific Substances (AREA)

Abstract

L'invention concerne un procédé de neutralisation d'un écoulement d'acide qui consiste: a) à faire passer l'écoulement d'acide et l'hydroxyde de calcium dans une première zone de réaction, de préférence un réacteur à écoulement idéal (1), jusqu'à une seconde zone de réaction, de préférence un réacteur à bac à agitation (12), de façon que l'hydroxyde de calcium neutralise partiellement l'écoulement d'acide lors de son déplacement vers la seconde zone de réaction, cette dernière étant équipée de moyens pour mesurer le pH de la solution dans la seconde zone de reáction (14) et pour alimenter la seconde zone de réaction en base aqueuse. L'appareil selon l'invention se compose d'un réacteur à écoulement idéal (1) comprenant des moyens d'alimentation en acide (4) et hydroxyde de calcium (8) grâce à une commande de dosage à action directe (7), d'un réacteur à bac à agitation (12) équipé de moyens pour mesurer le pH de la solution dans cette zone (14), d'une alimentation en base aqueuse (15) et d'un moyen de commande à action directe (17) conçu pour réguler l'alimentation en base aqueuse.
EP93918055A 1992-08-24 1993-08-19 Procede et appareil de neutralisation d'ecoulement d'acide Withdrawn EP0655986A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB929217962A GB9217962D0 (en) 1992-08-24 1992-08-24 Process and apparatus for neutralisation of acid streams
GB9217962 1992-08-24
PCT/GB1993/001762 WO1994004467A1 (fr) 1992-08-24 1993-08-19 Procede et appareil de neutralisation d'ecoulement d'acide

Publications (1)

Publication Number Publication Date
EP0655986A1 true EP0655986A1 (fr) 1995-06-07

Family

ID=10720858

Family Applications (1)

Application Number Title Priority Date Filing Date
EP93918055A Withdrawn EP0655986A1 (fr) 1992-08-24 1993-08-19 Procede et appareil de neutralisation d'ecoulement d'acide

Country Status (5)

Country Link
EP (1) EP0655986A1 (fr)
JP (1) JPH08500523A (fr)
CA (1) CA2139441A1 (fr)
GB (1) GB9217962D0 (fr)
WO (1) WO1994004467A1 (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6080910A (en) * 1997-02-20 2000-06-27 Case Western Reserve University Transgenic knockout animals lacking IgG3
JP5541595B2 (ja) * 2010-01-26 2014-07-09 パウダーテック株式会社 有機系脱酸素剤
JP5871026B2 (ja) * 2014-05-13 2016-03-01 住友金属鉱山株式会社 硫酸酸性溶液の中和方法、およびニッケル酸化鉱石の湿式製錬方法
EP3351513A1 (fr) * 2017-01-20 2018-07-25 Covestro Deutschland AG Procédé et dispositif de neutralisation d'acide chlorhydrique en continu
CN115896830A (zh) * 2023-02-16 2023-04-04 凯莱英生命科学技术(天津)有限公司 反应釜及具有其的电化学反应装置

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3638023C2 (de) * 1986-11-07 1997-08-14 Semmelroth Reinhold Anlage zur Behandlung industriellen Abwassers
JPH03196895A (ja) * 1989-12-26 1991-08-28 Yajima Takehiko 中和及び酸性化防止処理剤並びにその製造方法

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9404467A1 *

Also Published As

Publication number Publication date
JPH08500523A (ja) 1996-01-23
CA2139441A1 (fr) 1994-03-03
WO1994004467A1 (fr) 1994-03-03
GB9217962D0 (en) 1992-10-07

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