DE202018101963U1 - Plant for sludge-reduced lime water production and pre-treatment by acid decarbonization - Google Patents

Abstract

Plant for producing lime water from lime milk and dissolving water, with an apparatus (1, 2, 4, 5) for decarbonating the dissolving water and a plant part (6, 8, 9) for producing the lime water by dissolving the lime in the decarbonated dissolving water, characterized characterized in that the apparatus (1, 2, 4, 5) for decarbonating the dissolving water comprises an acid dosage (1) and a downstream device (2, 4, 5) for degassing carbon dioxide from the dissolving water.

Description

The invention relates to a plant for producing lime water from lime milk and dissolving water, with an apparatus ( 1 . 2 . 4 . 5 ) for decarbonating the dissolving water and a plant part ( 6 . 8th . 9 ) for producing the lime water by dissolving the milk of lime in the decarboxylated dissolving water.

State of the art

Lime water is used in drinking, process and process water treatment (for example in the food industry and in breweries) to deacidify, harden or even soften water.

The active ingredient of lime water is dissolved alkaline calcium hydroxide which reacts with acidic water components.

For the production of lime water lime milk is needed, which can either be purchased as a finished product or can be prepared by the application of hydrated lime or extinguishing quicklime. The milk of lime is a supersaturated calcium hydroxide suspension containing undissolved calcium hydroxide and insoluble matter. Kalkwasser is a calcium hydroxide solution that is largely free of turbidity and undissolved constituents.

To make lime water from lime milk, the suspension is diluted with water (dissolving water) in a dedicated reactor (dissolving process).

Part of the calcium hydroxide reacts with the inorganic carbon dissolved in the water (in the form of carbon dioxide CO ₂ and bicarbonate HCO ₃ ^- ). This process produces insoluble precipitation products (calcium carbonate and magnesium hydroxide). The amount of precipitated products is significantly influenced by the nature of the dissolution water.

These precipitated products and insoluble constituents from the milk of lime must be separated from the lime water before the clear lime water can be used (solids separation).

The solids separation of the undissolved substances from the lime water can be achieved by sedimentation in so-called lime saturators, conventional depth filtration, ultrafiltration or microfiltration or flocculation with subsequent sedimentation, e.g. done with inclined slaughter clarifiers.

The procedural design of the separation process depends on the concentration of the insoluble constituents and thus depends on the nature of the dissolving water. The size of the separation stage significantly influences the investment costs of the entire system. At high solids concentrations, the filter speed drops in filtration processes, the filter runtime decreases and the rinsing water requirement increases. Sedimentation processes reduce the possible surface load as well as the degree of separation. In both cases, this increases the size of the required equipment of the separation stage.

The solids-rich sludge separated by the separation apparatus is a residue of lime water production. To reduce the amount of sludge this can be further thickened.

The dissolving water can be pretreated to reduce the proportion of dissolved inorganic carbon (in the form of carbon dioxide CO ₂ and bicarbonate HCO ₃ ^- ) and thus the amount of precipitates in the dissolving process. However, the use of these processes for desalting the dissolving water (for example reverse osmosis) is very expensive (high investment costs, very high operating costs due to high energy input, usually the use of an antiscalant required, accumulation of saline concentrate, which must be disposed of).

Further measures for reducing the Kalkwasserverbrauchs and Kalkschlammanfalls are not known from the prior art.

Task and solution of the invention

OBJECT OF THE INVENTION: The above-mentioned disadvantages of the prior art are to be avoided.

This object is achieved according to the invention in a plant for the production of lime water from lime milk and dissolving water of the type mentioned above, in that the apparatus ( 1 . 2 . 4 . 5 ) for the decarbonization of the dissolving water, an acid dosage ( 1 ) and a downstream facility ( 2 . 4 . 5 ) for the outgassing of carbon dioxide from the dissolving water.

The plant makes it possible to significantly reduce the amount of sludge in the production of lime water by treating the water with acid decarbonization.

Advantages of the Invention Compared to Methods Without Dissolution Water Pretreatment

1) Reduction of the amount of lime needed to produce the lime water by reducing the precipitation processes.

By pretreating the dissolving water by means of acid decarbonization, the dissociation equilibrium of carbonic acid in the dissolving water is initially shifted by acid metering (such as hydrochloric acid, sulfuric acid or nitric acid, for example) to a pH of about pH 4.3. At this pH, about 99% of inorganic carbon is dissolved CO ₂ . The acid requirement of the water to achieve the desired pH depends on the acid capacity of the raw water.

Subsequent physical deacidification, ie outgassing of the free carbonic acid (CO ₂ ), largely removes the inorganic carbon (in the form of carbon dioxide CO ₂ and bicarbonate HCO ₃ ^- ) from the water.

The pretreatment of the dissolution water by means of acid decarbonization reduces the consumption of lime milk, since the demand for calcium hydroxide for the precipitation reaction with CO ₂ and HCO ₃ ^{- is} considerably reduced. Consequently, the calcium hydroxide in the saturator can dissociate for the most part in the dissolving water and remains stable in solution.

2) Substantial reduction of sludge accumulation (calcium carbonate and magnesium hydroxide) and thus reduction of recovery / disposal costs.

The pre-treatment of the dissolution water by means of acid decarbonization ensures that the precipitation products of the reaction between lime water and inorganic carbon are considerably reduced in their quantity. After solids separation (e.g., by filtration) and further thickening, sludge accumulation for lime water treatment is greatly reduced compared to conventional plants.

3) Reduction of the technical effort for solids separation, i. lower deposition requirement due to the reduced amount of precipitated products.

By reducing the precipitation of the technical effort for the solids separation is significantly reduced.

In the case of a filtration stage as a separation apparatus, this means that the dimensions of the filter can be made smaller, the filter run time is extended, that is, the filter must be backwashed less frequently and the pressure drop during the filtration process increases more slowly, resulting in a lower energy consumption and a lower Rinse water volume has the consequence.

In other separation processes, the lower particle load also offers advantages in terms of process design, process efficiency and energy consumption.

4) Ensuring a high quality of the lime water.

Due to the reduction of the precipitation products and the insoluble components in the discharge of the saturator, the downstream separation process is less burdened, which has an advantageous effect on the quality of the lime water. By way of example, for a sedimentation stage, with a low particle load, a lower discharge turbidity is to be expected than would be the case with a high particle load.

5) Low wastewater through an optional recirculation and thus a reduction in the cost of recovery / disposal.

Through a possible return of the clear water in the inflow of the dissolving process as residue almost exclusively a dewatered sludge (minimization of wastewater).

Advantages of the Invention over Alternative Methods for Dissolving Water Pretreatment According to the Prior Art (Reverse Osmosis)

6) Significant reduction of equipment costs

In the case of pre-treatment of the dissolving water by reverse osmosis certain components are to be provided, which are responsible for a large proportion of the system costs. These include in particular the membrane racks, pressure pipes, reverse osmosis modules and high-pressure pumps.

In contrast, in the case of the dissolution water pretreatment according to the invention by an acid decarbonization, comparatively low investment costs are to be expected (only metering device, measuring and regulating device, chemical container).

7) Significant reduction in operating costs (electricity)

Reverse osmosis is an energy-intensive process due to the high osmotic pressure to be overcome. The high power consumption of the high-pressure pumps is responsible for high energy costs, on the other hand a corresponding connection to the power grid is required, which may need to be realized first.

Further operating costs arise from the regular replacement of the reverse osmosis modules.

In the solution water pretreatment according to the invention by an acid decarbonization, the operating costs are limited to the acid and the energy costs for the gas exchange.

8) Avoidance use of antiscalants

Reverse osmosis systems concentrate the water ingredients as efficiently as possible to make efficient use of water resources. At these concentrations, however, the solubility of some salts is locally exceeded, resulting in a mineral layer on the membrane surface. This massively limits the permeability of the membrane and must therefore be prevented. This is achieved with the addition of crystallization inhibitors, so-called antiscalants, which increases the solubility of corresponding salts or retards the crystallization of these.

Apart from the acid, no further use of chemicals is required in the case of the acidic decarbonization according to the invention.

9) Prevention of concentrate accumulation, which must be disposed of

The concentrate resulting from reverse osmosis must be disposed of. The introduction into the sewage system is usually associated with very high costs and is often undesirable from the process engineering side of the wastewater treatment plant operator. For the discharge into a receiving water, an official permit is necessary, which depends on the concentrate components and the water quality of the receiving water. Particularly for low-flow sewer systems, the permitability of the project must be considered critically. In addition, depending on the distance to the receiving water a long piping is needed. The construction of such a route also requires official approval.

The preparation of the concentrate to achieve regulatory approval requires further technical steps and is costly in addition to the construction of the route.

10) Ecological benefits (energy saving, no entry of antiscalants into aquatic environment)

In the system according to the invention, in contrast to the release water production by reverse osmosis, no energy-intensive high-pressure pumps needed. The saved electrical energy, which mostly comes from fossil primary energy sources, helps to reduce the emission of climate damaging CO ₂ .

Furthermore, no concentrate flow is applied, which is offset with antiscalant. This can adversely affect the ecological status of the receiving water.

Overcome technical difficulties

The inventor has overcome the following technical difficulties in a non-obvious way in the development of the plant according to the invention.

Natural water usually contains a buffer system of free carbonic acid, bicarbonate and bicarbonate. These species of dissolved inorganic carbon can be converted into each other depending on the pH and acid or alkali addition. Thus, the addition of basic calcium hydroxide is buffered. Dissolved calcium hydroxide does not appear appreciably until all of the inorganic carbon has been converted to sparingly soluble calcium carbonate. Therefore, usually a larger amount of calcium hydroxide must be dosed, as later in the lime water is present, and this proportion is obtained as an undesirable by-product in the form of sludge (calcium carbonate and magnesium hydroxide).

In the design of the sludge-reduced lime water production plant, in the first two process steps the dissolved inorganic carbon (in the form of carbon dioxide CO ₂ and hydrogen carbonate HCO ₃ ^- ) is removed from the water. As a result of the addition of acid, in the first step the chemical equilibrium of the dissolving water is shifted so that about 99% of the dissolved inorganic carbon is present as dissolved CO ₂ . Since this is in equilibrium with the CO ₂ in the air, this can be largely removed by a gas exchange from the water.

For a dissolving water without this buffer system, the above-mentioned technical and economic advantages for Kalkwasserherstellung arise. Compared to a dissolution water pretreatment with reverse osmosis, the use of acid decarburization offers considerable advantages.

Advantageous embodiments of the invention are set forth in the subclaims.

embodiment

In the following an embodiment of the invention will be described in more detail with reference to a drawing.

It shows 1 the inventive plant for sludge-reduced Kalkwasserherstellung according to an embodiment.

In the first step, acid (such as hydrochloric acid, sulfuric acid, nitric acid or the like) is metered into the raw water in order to set a pH of, for example, 4.3. Thus, the dissolved inorganic carbon is predominantly present as dissolved CO ₂ .

In an apparatus for removing carbon dioxide 2 (Eg column, Flachbettbelüfter, membrane degassing or the like), the dissolved CO _{2 is} largely removed (if possible, <3 mg / l). For gas exchange, air or other carrier gas can be used and it can be applied to the exhaust port of the apparatus, a vacuum, this is especially true for the membrane degassing with a membrane contactor.

To prepare lime water, ready-to-use lime milk can be placed in a container 6 be used. Alternatively, the milk of lime can also be produced on site.

The dissolving water and the lime milk 7 become lime water production 8th mixed and into a saturator (residence time container) 9 where the calcium hydroxide contained in the milk of lime is dissolved. For the reaction and dissolution time, for example, between 3 and 8 minutes are desirable. The residence time behavior should, if possible, be designed so that a piston flow is achieved and short circuit flows are largely excluded. Possibly. is to ensure a certain energy input for homogenization and to avoid sedimentation of particles.

There are various variants for removing the insoluble constituents and the precipitated products from the lime water:

The process for solids separation can be realized in different ways:

Probably the most cost-effective variant is a Kalkwasserfiltration with conventional depth filter 10 (eg as a sand or multi-layer filter).

The overflow of the filter can also be used as a residence time container. The backwash 13 takes place with lime water through the flushing water pump 12 from the storage container 11 , Flushing with air / compressed air is only possible in exceptional cases (avoiding carbonation). It is a muddy water treatment 15 required (eg settling tank with recirculation of the clear water 16 for Kalkwasserherstellung before reaction tank and thickener / sludge dewatering).

• - Ultra- oder Mikrofiltration mit Membranen aus Keramik oder Polymer; beste Kalkwasserqualität, aber relativ aufwendig und nur mit regelmäßigen Säurespülungen möglich (z.B. dreimal täglich) mit anschließender Neutralisation.
• - Rückspülung mit Kalkwasser aus dem Vorlagebehälter. Es ist eine Schlammwasserbehandlung erforderlich (z.B. Absetzbecken mit Rückführung des Klarwassers zur Kalkwasserherstellung vor Reaktionsbecken und Eindicker / Schlammentwässerung).
• - Rückspülbare Automatikfilter.
• - Abtrennung mittels Kompaktflockungsanlage und Absetzanlage (Lamellenklärer); bei Bedarf mit Schlammentwässerung / Nacheindickung und ggf. mit Rückführung des Klarwassers zur Kalkwasserherstellung vor Reaktionsbecken).
• - Abtrennung in einem Kalksättiger.
• - Einsatz anderer Verfahren zur Partikelabtrennung.

Alternative methods for removing the insoluble matter and precipitates from the lime water are:

• - Ultra or microfiltration with ceramic or polymer membranes; best Kalkwasserqualität, but relatively expensive and only with regular acid rinses possible (eg three times a day) with subsequent neutralization.
• - Backwashing with lime water from the storage tank. It is a sludge water treatment required (eg settling tank with recycling of clear water for Kalkwasserherstellung before reaction tank and thickener / sludge dewatering).
• - Backwashable automatic filter.
• - Separation by Kompaktflockungsanlage and settling plant (lamella clarifier); if necessary with sludge dewatering / re-thickening and if necessary with return of the clear water for lime water production in front of reaction tanks).
• - Separation in a Kalksättiger.
• - Use of other methods for particle separation.

• - Alle Behälter mit aufbereitetem Lösewasser, Kalkmilch und Kalkwasser sollten gegen übermäßigen Luftaustausch (CO₂-Zufuhr) geschützt werden.
• - Alle Anlagenteile mit Kalkmilch / Kalkwasser sollten für Reinigungsprozesse gut zugänglich sein bzw. mit einer automatischen Reinigungsanlage ausgestattet sein.

Other requirements / notes:

• - All containers of treated dissolving water, lime and lime water should be protected against excessive air exchange (CO ₂ supply).
• - All plant components with lime / lime water should be easily accessible for cleaning processes or equipped with an automatic cleaning system.

As a method for sludge treatment, all common methods for sludge-covering such as sedimentation, drainage in containers or similar. be used. The recirculation of the resulting clear water into the process substantially minimizes or completely eliminates the build-up of basic wastewater.

Comparative Example: Annex known from the prior art:

Without pretreatment by addition of acid and aeration, the dissolved inorganic carbon remains in the dissolving water. When lime milk is added, the calcium hydrogen carbonate contained therein reacts with the dissolved carbon dioxide or bicarbonate to form calcium carbonate, which precipitates and contributes significantly to the sludge mass. This reaction also takes place when lime hydrate is applied or lime is extinguished if non-carbonated water is used as the leaching water. Therefore, a larger amount of lime milk is required for the same amount of lime water produced, as it is the case in the inventive system.

Also, the stage for particle separation must be made considerably more expensive in the absence of pre-treatment of the dissolving water. In the case of depth filtration for particle separation, it must be dimensioned larger at a high particle concentration, in contrast to the example according to the invention. Otherwise, the filter would already have a short runtime quality after a short runtime and quickly build up a high differential pressure. In any case, a large amount of flushing water is required to remove the high amount of sludge in the filter.

For the separation process ultrafiltration and microfiltration, a larger dimensioning is necessary, otherwise is to be expected with a rapidly increasing differential pressure. Again, the amount of flushing water increases with the increased particle concentration.

In the case of a flocculation system for particle separation, a larger amount of chemicals is required in addition to the larger dimensions.

Compared to reverse osmosis pre-treatment with water, the use of acid decarburization offers considerable advantages (saving of investment costs and operating costs, avoidance of concentrates, ecological benefits).

Further advantageous embodiments of the invention

Possibility to retrofit the system according to the invention for existing systems. This results in the possibility of using poorer and thus cheaper types of lime and a lower turbidity of the lime water

In particular, by the use of a conventional filtration to remove the insoluble constituents from the lime water, a particularly cost-effective variant is ensured.

The developed system is automatable.

The cleaning effort is reduced by the reduced amount of sludge.

LIST OF REFERENCE NUMBERS

1

acid dosage

2

Apparatus for removing carbon dioxide

3

Decarbonated solvent water

4

Air or carrier gas supply

5

exhaust

6

Kalkmilchbehälter

7

addition of lime

8th

lime water

9

Saturator (residence time container)

10

Apparatus for separating particles

11

storage container

12

irrigation pump

13

dishwater

14

muddy water

15

Sludge water treatment

16

Clear water recirculation

17

Kalkwasserdosierung

Claims (7)

Plant for producing lime water from lime milk and dissolving water, with an apparatus (1, 2, 4, 5) for decarbonating the dissolving water and a plant part (6, 8, 9) for producing the lime water by dissolving the milk of lime in the decarbonated dissolving water, characterized characterized in that the apparatus (1, 2, 4, 5) for decarbonating the dissolving water comprises an acid dosage (1) and a downstream device (2, 4, 5) for degassing carbon dioxide from the dissolving water. Plant for producing lime water from lime milk and dissolving water after Claim 1 , characterized in that a sludge water treatment (15) with a clear water return (16) for Kalkwasserherstellung (8) and / or to a saturator (9), which is the lime water production (8) connected downstream, is provided. Plant for producing lime water from lime milk and dissolving water after Claim 1 , characterized in that for the separation of solids a Kalkwasserfiltration with conventional depth filter (10) is used. Plant for producing lime water from lime milk and dissolving water after Claim 1 , characterized in that the containers are treated with treated solvent water, milk of lime and lime water protected against excessive air exchange and CO ₂ supply. Plant for producing lime water from lime milk and dissolving water after Claim 1 , characterized in that the plant parts with lime / Kalkwasser for cleaning processes well accessible or equipped with an automatic cleaning system. Plant for producing lime water from lime milk and dissolving water after Claim 1 , characterized in that a retrofitting of existing existing systems with the system according to the invention is possible. Plant for producing lime water from lime milk and dissolving water after Claim 1 , characterized in that the system can be automated.

Images