Process and plant for recycling chromate-containing lithium bromide solutions from cold absorption systems

Abstract

The invention relates to a method and a device for recycling lithium bromide solutions containing chromate from cold absorption systems, wherein barium bromide is added to a lithium chromate-containing lithium bromide solution and the chromate to be removed is replaced by bromide, in that lithium bromide is directly produced from the lithium chromate according to the formula: Ba 2+ + 2 Br - + 2 Li + + CrO4 2- → BaCrO4 (s) + 2 Li + + 2 Br - is generated. The plant has at least one stirred tank (1), wherein the stirred tank has a common or separate feed for lithium chromate-containing lithium bromide solution, barium bromide and activated carbon, as well as an air supply, a vent and a stirrer, and a discharge for the reaction product from the tank.

Description

[0001] Absorption chillers (ACCs) are the most ecologically and economically sound solution for many refrigeration and air conditioning applications. This is especially true when unused heat sources can be utilized (e.g., waste heat from combined heat and power plants or waste incineration plants) or when the heat comes from renewable energy sources (solar thermal).

[0002] Absorption cooling utilizes the temperature dependence of the physical solubility of two substances (the so-called working fluid pair). The most common working fluid pair is water / lithium bromide (LiBr). Depending on the cooling capacity, these absorption chillers typically use fill quantities ranging from a few hundred kilograms to several tons of a 54% lithium bromide solution.

[0003] Currently, used materials are disposed of after the end of the AKA's service life or following accidents, thus removing the LiBr from the cycle. This also results in the loss of lithium, a metal strategically valuable for various future technologies. Furthermore, Germany's current demand for lithium bromide solution must be met entirely through imports.

[0004] In order to suppress the problem of corrosion on the metallic components in contact with the solution in AKA, especially under high thermal loads up to 180 °C, so-called corrosion inhibitors are added to the LiBr absorption solution.

[0005] Until the end of the 20th century, this was primarily lithium chromate. With the enactment of the Hazardous Substances Ordinance of 2005 (GefStoffV 2005), chromate was classified as a hazardous substance (category 4) due to its toxicity and classification as a carcinogenic substance. This entailed extensive protective measures and restrictions on the handling of chromate, culminating in the inclusion of eight chromates in Annex XIV of the REACH Regulation as SVHCs (Substances of Very High Concern). A mandatory substitution assessment also applies to these high-risk substances. After the sunset date of September 21, 2017, companies may no longer use these eight substances without EU authorization.

[0006] Patent CN00232311 describes a mechanical processing method using a specific machine arrangement. However, the solution described there does not address the removal of chemical additives, such as inhibitors. Another patent specification for filtering lithium bromide solution is JPH09236358A. This, however, also relates only to the removal of solid components from an existing salt solution.

[0007] Removing the chromate corrosion inhibitor present in the lithium bromide solution is not possible with the two aforementioned solutions and has not been practiced to date. For this reason, such solutions have had to be disposed of.

[0008] This led to the task of developing a process and a plant for recycling chromate-containing LiBr solutions (lithium bromide solutions) from cold absorption systems, whereby a chromate inhibitor removal from LiBr solutions is implemented in order to prepare these solutions for reuse.

[0009] This problem is solved using the features of claims 1 and 6.

[0010] Advantageous embodiments result from the dependent claims.

[0011] In the inventive process for recycling chromate-containing lithium bromide solutions from cold absorption systems, barium bromide is added to a lithium chromate-containing lithium bromide solution and the chromate to be removed is replaced by bromide, by directly producing lithium bromide from the lithium chromate according to the formula: Ba 2+ + 2 Br - + 2 Li + + CrO4 2- → BaCrO4 (s) + 2 Li ++ 2 Br - is generated.

[0012] Advantageously, the removal of the interfering ion in the form of chromate simultaneously increases the active ingredient content of LiBr.

[0013] Preferably, activated carbon is added to a mixture of lithium bromide solution containing lithium chromate and barium bromide in a stirred tank with the addition of air. The mixture is stirred with the addition of air, then drained from the tank and passed through at least one condenser to cool. The liquid is then filtered in at least one filtration system to remove solids, and the lithium bromide solution, now free of chromate and solids, is withdrawn and reused.

[0014] It is possible, after filtration, to return a lithium bromide solution containing solids to the circulation process and continue this circulation until a clear lithium bromide solution is obtained. Preferably, a visual inspection after the filtration system is used to assess whether the lithium bromide solution is sufficiently clear.

[0015] According to the procedure, the container is preferably first supplied with the lithium bromide solution containing lithium chromate, then with barium bromide and subsequently with activated carbon, for example via a feeder or via separate feeders.

[0016] Air is introduced into the container via an air supply, preferably a submersible line. Exhaust air is extracted from the upper part of the container.

[0017] The inventive system for recycling lithium bromide solutions containing lithium chromate from cold absorption systems has at least one stirred tank, wherein the stirred tank has a common or separate feed for lithium chromate-containing lithium bromide solution, Barium bromide and activated carbon as well as an air supply a vent, and a stirrer as well as a drain for the reaction product from the container.

[0018] The downstream section is connected to a cooler, or a cooler is integrated into the downstream section, in which the reaction product is cooled.

[0019] The system advantageously includes at least one filter for removing solids from the reaction product, which is arranged downstream of the cooler. A sampling point may be provided downstream of the filter.

[0020] Furthermore, at least one means for controlling the turbidity of the chromate-free lithium bromide solution should be provided.

[0021] For this purpose, a sight glass / flowmeter is integrated into the pipe after the filter(s) have passed through.

[0022] The system according to the invention is explained in more detail below with reference to a drawing.

[0023] It shows Fig. 1. The basic diagram of the system.

[0024] The system has a modular design. The individual components are used depending on the task at hand.

[0025] The system consists of the following components: - at least one stirred tank 1, preferably made of PE - polyethylene with dry material dosing, a feed 1.1 for lithium bromide solution containing chromate, for lithium bromide and activated carbon, an air supply 1.2, an outlet 1.3 for exhaust air, a level detection 1.4 and an agitator 1.5, as well as an outlet 1.6 for the reaction product, at least one filter system 2, here with two redundant filter housings 2.1, 2.2 for the removal of solids such as impurities and lithium carbonate which may be formed during concentration. - optionally a cooling unit 3, whereby heat is generated during concentration in the mixing vessel 1. It is advantageous that the solubility of precipitates decreases in the cold or at lower temperatures. - a first temperature sensor 4.1, which is arranged between mixing vessel 1 and cooling unit 3 - a second temperature sensor 4.2, which is arranged after the cooling 3 and, as shown in the figure, is positioned after the filter system 2, a sight glass / flowmeter 5 for visual inspection of the reaction product (lithium bromide solution which no longer contains chromate), unlabeled pumps and valves.

[0026] As a standard procedure, the first step involves verifying information provided by the waste producers (e.g., existing certificates of analysis) and conducting analyses of the solution using rapid tests or an external laboratory. This analysis focuses primarily on the lithium bromide concentration, the identification of any inhibitors (chromate, etc.), and impurities (e.g., inorganic suspended solids, organic impurities). The results determine whether reprocessing the solution into one suitable for reuse in absorption chillers is technically feasible and economically viable, or whether additional LiBr concentration is necessary.

[0027] The following is a sample procedure: Example:

[0028] 1000 L of a used 7% LiBr solution was examined for organic impurities. These were determined as TOC at 600 mg / L. The chromium concentration (present as chromate) was determined to be 130 mg / L. The solution was filled into reaction vessel 1 via feeder 1.1 and stirred for approximately 30 minutes with agitator 1.5, driven by motor M, while air was introduced via air inlet 1.2. Exhaust air escaped through air outlet 1.3. After the addition of 322 mL of 23% barium bromide solution and 500 g of finely powdered activated carbon (also via feeder 1.1), the mixture was mixed again for approximately 30 minutes using agitator 1.5 in the stirred vessel 1.

[0029] The fill level in the mixing vessel 1 can be checked using the fill level detection 1.4.

[0030] After completion of the stirring process, the suspension / reaction product was drained via outlet 1.6 into an unnamed line and forced through the filter system 2, whereby the reaction product had to pass through a cooling unit 3, which cooled it down.

[0031] After passing through the filter system, the reaction product can be removed or, after inspection using the sight glass / flowmeter 5, returned to the stirred tank 1 and from there passed through the cooling unit 3 and the filter system 2 again until the reaction product is clear.

[0032] By utilizing the filter aid properties to build up a fine-pored filter cake in combination with cooling the solution to below 20°C, an excellent result was surprisingly achieved, yielding a lithium bromide solution that contained no chromate or a negligible amount of chromate.

[0033] It is possible to divide the system into two trays, as indicated by the dividing lines T.

[0034] Using barium bromide, the chromate to be removed could be replaced by bromide, and lithium bromide is essentially generated directly from the lithium chromate. Here, the interfering ion "chromate" is removed directly from the solution, and the concentration of the active ingredient LiBr is simultaneously increased. Ba 2+ + 2 Br - + 2 Li + + CrO4 2- → BaCrO4 (s) + 2 Li + + 2 Br -

[0035] The chromate concentration decreases as the reaction mixture is kept colder, with an integrated cooler dissipating the heat. For barium chromate, the solubility product (Ksp) at 28°C is 2.4 × 10⁻⁶. -10 The value is specified. Even at just 25°C, the value reduces to 1.17×10 -10 .

[0036] Analysis of the chromium concentration (dissolved chromate) in the solution before the addition of activated carbon and before cooling revealed a reduction to 0.37 mg / L. Utilizing cooling and the use of activated carbon further reduced the Cr content of the treated LiBr solution to only 0.2 mg / L, representing a reduction of 99.85%. The TOC was determined to be only 20 mg / L.

[0037] For reuse in cold absorption systems, this purified 7% solution was adjusted to the usual concentration of 50 to 55% using 100% LiBr salt. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] CN 00232311

[0006]

Claims

[1] Method for recycling chromate-containing lithium bromide solutions from cold absorption systems, wherein barium bromide is added to a lithium chromate-containing lithium bromide solution and the chromate to be removed is replaced by bromide by directly producing lithium bromide from the lithium chromate according to the formula: Ba 2+ + 2 Br - + 2 Li + + CrO4 2- → BaCrO4 (s) + 2 Li + + 2 Br - is generated. [2] Method according to claim 1, characterized by that by removing the interference ion chromate, the active ingredient content of LiBr is simultaneously increased. [3] Method according to claim 1 or 2, characterized by, in which activated carbon is added to the mixture of lithium chromate-containing lithium bromide solution and barium bromide in a stirred vessel (1) with the supply of air, everything is stirred with the supply of air, then passed through at least one cooler (2) and cooled and subsequently filtered in at least one filter system, removing solids and in which the lithium bromide solution freed from chromate and solids is withdrawn and reused. [4] Method according to claim 3, characterized by , that a lithium bromide solution containing solids after filtering is added back to the container so that circulation takes place until a clear solution is present. [5] Method according to any one of claims 1 to 3, characterized by , that - first lithium chromate-containing lithium bromide solution and - then barium bromide - then activated carbon is added to the container [6] Apparatus for recycling lithium bromide solutions containing lithium chromate from cold absorption systems and for carrying out the method according to any one of claims 1 to 5, characterized by that the plant has at least one mixing vessel (1), wherein the mixing vessel has a common or separate feed for lithium chromate-containing lithium bromide solution Barium bromide activated carbon has as well as an air supply a vent and a stirrer and a drain for the reaction product from the container. [7] Device according to claim 6, characterized by , that the discharge is connected to a cooler in which the reaction product is cooled. [8] Device according to claim 6 or 7, characterized by that it has at least one filter for removing solids from the reaction product. [9] Device according to claim 8, characterized bythat the system has devices for controlling the turbidity of the liquid dispensed from the container after passing through the filter(s).

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