Implementation of online measurement in a sodium cyanide production plant

Abstract

Apparatus for carrying out a process for the production of alkali metal cyanide using gaseous hydrogen cyanide, hydrogen cyanide-containing gas or liquid hydrogen cyanide and an aqueous alkali metal hydroxide solution, comprising a) a conduit for transporting a liquid formed during the process, selected from an aqueous alkali metal cyanide solution or an aqueous alkali metal cyanide suspension and b) a system for online determination of one or more process parameters of the liquid transported through the pipeline, which serve for process control of the procedure, wherein the system comprises b1) a refractometer for measuring the refractive index of the liquid formed, wherein the refractometer or part thereof is arranged in the line for contact with the liquid, (b2) an ultrasonic measuring device for determining the mass flow rate of the liquid, wherein the ultrasonic measuring device is arranged outside the line without contact with the liquid, wherein the refractometer and the ultrasonic measuring device are configured to communicate with each other and exchange data, b3) one or more computing units configured to receive the readings from the refractometer and the ultrasonic measuring device, and the computing unit(s) configured to use the received readings from the refractometer and the ultrasonic measuring device to determine one or more process parameters of the liquid.

Description

[0001] The invention relates to a plant for carrying out a process for the production of alkali metal cyanide using gaseous hydrogen cyanide, hydrogen cyanide-containing gas or liquid hydrogen cyanide and an aqueous alkali metal hydroxide solution.

[0002] In process plants for the production of sodium cyanide solutions and sodium cyanide suspensions, it is currently not possible to simultaneously determine the sodium hydroxide (NaOH) and sodium cyanide (NaCN) content using standard online measuring instruments. This is only possible through offline laboratory measurements, which means that changes in the plant conditions can only be addressed with a time delay.

[0003] The state of the art involves online measurement of mass flow rate, density, and temperature using a mass flow meter and, if necessary, turbidity measurement using an online refractometer. The NaOH and NaCN content can only be measured offline in a laboratory.

[0004] The object of the present invention was therefore to provide a system with a measuring arrangement that enables simultaneous online measurement of the alkali metal hydroxide and alkali metal cyanide content in a reaction liquid formed during the production of alkali metal cyanide. The online determination of other process parameters of the reaction liquid should also be possible. The online determined process parameters serve in particular for the rapid, online control of the process and its operating conditions.

[0005] This problem could be solved by an apparatus for carrying out a process for the production of alkali metal cyanide using gaseous hydrogen cyanide, hydrogen cyanide-containing gas or liquid hydrogen cyanide and an aqueous alkali metal hydroxide solution, comprising a) a conduit for transporting a liquid formed during the process, selected from an aqueous alkali metal cyanide solution or an aqueous alkali metal cyanide suspension and b) a system for online determination of one or more process parameters of the liquid transported through the pipeline, which serve for process control of the procedure, wherein the system comprises b1) a refractometer for measuring the refractive index of the liquid formed, wherein the refractometer or part thereof is arranged in the line for contact with the liquid, b2) an ultrasonic measuring device for determining the mass flow rate of the liquid, wherein the ultrasonic measuring device is arranged outside the pipe without contact with the liquid, b3) one or more computing units configured to receive the readings from the refractometer and the ultrasonic measuring device, and the computing unit(s) configured to use the received readings from the refractometer and the ultrasonic measuring device to determine one or more process parameters of the liquid.

[0006] Preferred embodiments are described in the dependent claims.

[0007] The system according to the invention enables the simultaneous online determination of the content of alkali metal hydroxide, preferably NaOH, and alkali metal cyanide, preferably NaCN, online and in real time. This allows the process plants for the production of alkali metal cyanide solutions, preferably sodium cyanide solutions, and alkali metal cyanide suspensions, preferably sodium cyanide suspensions, to be adjusted more precisely and quickly to the desired quality parameters and also to be better automated.

[0008] The advantages of such an online measurement are: - the consumption of alkali metal hydroxide is reduced, - the production of alkali metal cyanide suspension becomes less prone to disruption, - the quality of the final product alkali metal cyanide powder improves.

[0009] The following special features of the system according to the invention come into play compared to the prior art: Permanent online measurement of the following parameters is possible: alkali metal hydroxide content (e.g., NaOH content) of the alkali metal cyanide content (e.g. NaCN content) of the mass flow density the temperature.

[0010] All online measurements can be used for control purposes. The Fig. Figure 1 shows a schematic diagram of an exemplary embodiment of the invention.

[0011] The invention is described in detail below.

[0012] The invention relates to an apparatus for carrying out a process for the production of alkali metal cyanide using gaseous hydrogen cyanide, hydrogen cyanide-containing gas or liquid hydrogen cyanide and an aqueous alkali metal hydroxide solution.

[0013] The alkali metal cyanide produced in the apparatus according to the invention is preferably sodium cyanide or potassium cyanide, particularly preferably sodium cyanide. Accordingly, the alkali metal hydroxide solution is preferably a sodium hydroxide solution or a potassium hydroxide solution, more preferably a sodium hydroxide solution.

[0014] The apparatus according to the invention comprises a line for transporting a liquid formed during the process, selected from an aqueous alkali metal cyanide solution or an aqueous alkali metal cyanide suspension.

[0015] In the apparatus according to the invention, an aqueous alkali metal cyanide solution is generally formed by the absorption of gaseous hydrogen cyanide, hydrogen cyanide-containing gas, or liquid hydrogen cyanide into an alkali metal hydroxide solution. Alkali metal cyanide can then be crystallized from the resulting alkali metal hydroxide solution in a subsequent apparatus, yielding an aqueous alkali metal cyanide suspension.

[0016] Generally, a first line transports the alkali metal cyanide solution into the crystallization apparatus, and a second line transports the aqueous alkali metal cyanide suspension out of the crystallization apparatus and to further processing.

[0017] Preferably, the first line and / or the second line are equipped with a system for the online determination of one or more process parameters of the liquid transported through the line. These process parameters can be used for process control of the procedure.

[0018] Process parameters are properties of the liquid transported through the pipeline that significantly influence the manufacturing process carried out in the plant. These include, for example, temperature, density, mass flow rate, alkali metal hydroxide content, and alkali metal cyanide content.

[0019] In a preferred embodiment, the one or more process parameters of the liquid to be determined include the alkali metal hydroxide content, the alkali metal cyanide content, the mass flow rate, the density, and the temperature.

[0020] Depending on the measured process parameters, intervention in the manufacturing process can be carried out, preferably in real time, to achieve the most stable production possible with high product quality. This process control can be automated by a process control system or manual by qualified operating personnel. Automated process control is preferred.

[0021] An intervention in the manufacturing process could be, for example, controlling the amount of alkali metal hydroxide solution added or its concentration.

[0022] In a preferred embodiment, the process control based on the determined process parameters includes the control of the alkali metal hydroxide solution content, particularly preferably the control of the sodium hydroxide solution content.

[0023] In a preferred embodiment, the online measurement essentially consists of the following two components: 1. A refractometer whose sensor or transmitter is installed in the pipeline. 2. An ultrasonic measuring device, which is attached to the outside of the pipeline in such a way that it does not touch the measuring medium, i.e. the liquid in the pipeline.

[0024] The refractometer and the ultrasonic measuring device are configured to communicate and exchange data. This makes it possible to process the measured values ​​obtained by one of the two measuring devices to determine the desired process parameters in the other measuring device.

[0025] The refractometer measures the refractive index of the liquid in the pipeline. Since the refractive index is temperature-dependent, a thermometer for determining the temperature is normally and preferably integrated into the refractometer. The thermometer can be any suitable measuring device for determining the temperature. A separate temperature measurement using a suitable thermometer is also possible. The refractometer exchanges the measured values ​​with the ultrasonic measuring device. If the temperature is determined using a separate thermometer and not one integrated into the refractometer, the measurement results from the separate thermometer are also transmitted to the ultrasonic measuring device. Preferably, however, a thermometer is integrated into the refractometer to measure the temperature of the liquid. The resulting measurement data can be transmitted to the processing unit associated with the ultrasonic device.

[0026] The liquid in the pipeline can be translucent to yellowish.

[0027] The refractometer exchanges measured values ​​with the ultrasonic measuring device and, based on the ultrasonic measuring device's readings and its own measurements (refractive index and preferably temperature), generates the alkali metal hydroxide content, preferably NaOH, and the alkali metal cyanide content, preferably NaCN. This exchange naturally occurs via the associated processing units.

[0028] Preferably, and unless otherwise specified, the content of alkali metal hydroxide or alkali metal cyanide in the liquid is given in mass percent.

[0029] The ultrasonic measuring device exchanges measured values ​​with the refractometer and, based on these values ​​and its own ultrasonic measurements, generates the mass flow rate through the pipeline, preferably in kg / h. The ultrasonic measuring device can also determine the density of the liquid, preferably in g / cm³. 3, and determine or output the temperature of the liquid, preferably in °C.

[0030] In the apparatus according to the invention, the refractometer is preferably used to determine the alkali metal hydroxide and alkali metal cyanide content using the refractive index and the data obtained from the ultrasonic measuring device. The alkali metal hydroxide and alkali metal cyanide content is preferably expressed as a percentage by mass.

[0031] An ultrasonic measuring device can generate sound waves, transmit them through a medium, such as a liquid, and receive them again. By measuring the transit times, the flow velocity can then be determined. From the measured flow velocity, the volumetric flow rate can be calculated using the pipe cross-section. The volumetric flow rate can then be converted into a mass flow rate, possibly with the aid of other parameters such as temperature and density.

[0032] In a preferred embodiment, the ultrasonic measuring device is attached to the outside of the cable.

[0033] The system according to the invention comprises one or more computing units configured to obtain the measured values ​​of the refractometer and the ultrasonic measuring device, and the computing unit(s) configured to determine one or more process parameters of the liquid using the obtained measured values ​​of the refractometer and the ultrasonic measuring device.

[0034] In a preferred embodiment, data processing takes place separately in the computing unit of the refractometer and in the computing unit of the ultrasonic measuring device.

[0035] The data measured by the refractometer and ultrasonic measuring device are received and processed in the processing unit(s) to determine the desired process parameters. It is preferred that the refractometer and the ultrasonic measuring device are each configured with at least one dedicated processing unit. In this case, at least one of the one or more processing units is assigned to or part of the refractometer, and at least one processing unit is assigned to or part of the ultrasonic measuring device.

[0036] Direct data exchange is possible between the refractometer's at least one processing unit and the ultrasonic measuring device's at least one processing unit. This allows the desired process parameters, such as alkali metal hydroxide content, alkali metal cyanide content, mass flow rate, density, and temperature, to be determined directly within the measuring devices' processing units. An external process control system is generally not required.

[0037] In a preferred embodiment, the one or more process parameters of the liquid to be determined are selected from the content of alkali metal hydroxide, the content of alkali metal cyanide, the mass flow rate, the density and the temperature, wherein the process parameters to be determined preferably include at least the content of alkali metal hydroxide and the content of alkali metal cyanide and particularly preferably all of the aforementioned process parameters.

[0038] Preferably, the temperature of the liquid transported through the pipe is determined in the refractometer using an integrated thermometer. The temperature measurement signal can then be transmitted to the ultrasonic measuring device. In the ultrasonic measuring device, the temperature can be used for further determination of process parameters and / or output by the device.

[0039] In a preferred embodiment, the sensor of the refractometer is located in the liquid to be measured, while the rest of the measuring instrument, in particular the computing unit, is located outside the pipe.

[0040] In a preferred embodiment, the one or more computing units comprise a first computing unit and a second computing unit configured to exchange data with each other, wherein the first computing unit is associated with the refractometer and is configured to determine the alkali metal hydroxide and alkali metal cyanide content in the liquid using the measurements obtained from the refractometer and the ultrasonic measuring device, and the second computing unit is associated with the ultrasonic measuring device and is configured to determine the mass flow rate of the liquid using the measurements obtained from the refractometer and the ultrasonic measuring device.

[0041] In a preferred embodiment, the ultrasonic measuring device outputs not only the mass flow rate but also the density and temperature of the liquid.

[0042] In a preferred embodiment, the system comprises i) a container for the absorption of gaseous hydrogen cyanide, hydrogen cyanide-containing gas or liquid hydrogen cyanide into the aqueous alkali metal hydroxide solution to form an aqueous alkali metal cyanide solution, ii) a device for crystallizing alkali metal cyanide from the alkali metal cyanide solution obtained in the container to form an aqueous alkali metal cyanide suspension, iii) a first conduit through which the aqueous alkali metal cyanide solution is transported from the container into the device, and iv) a second line through which the aqueous alkali metal cyanide suspension is transported from the apparatus, wherein the line for transporting the liquid formed during the process, and thus the line in / on which the system for measuring the process parameters is attached, is the first line or the second line.

[0043] All common, industrially applicable crystallizers are suitable as devices for crystallization. A preferred device for crystallization is an evaporative crystallizer. In a preferred embodiment, the device for crystallization is an evaporative crystallizer that is heated and operated under a vacuum.

[0044] In a preferred embodiment, the aqueous alkali metal cyanide suspension transported in the second line is subjected to a solid-liquid separation to obtain solid alkali metal cyanide.

[0045] The resulting solid alkali metal cyanide is preferably subjected to briquetting.

[0046] In a preferred embodiment, the crystallization device is an evaporative crystallizer which is heated and in which a vacuum is present, and / or the aqueous alkali metal cyanide suspension transported in the second line is subjected to solid-liquid separation to obtain solid alkali metal cyanide.

[0047] The alkali metal cyanide suspension formed in the crystallization apparatus can be further processed in a subsequent step to obtain, for example, solid alkali metal cyanide. Possible process steps include well-known solid-liquid separation methods such as filtration or centrifugation.

[0048] A process for the production of alkali metal cyanide using gaseous hydrogen cyanide, hydrogen cyanide-containing gas or liquid hydrogen cyanide in a plant according to the invention as described above is also disclosed, wherein one or more process parameters serving to control the process, in particular the content of alkali metal hydroxide and the content of alkali metal cyanide, in the liquid transported through the line are determined online in order to control the operating parameters of the process.

[0049] All information relating to the inventive system applies equally to this process, in particular with regard to the inventive system and the process, so reference is made to it.

[0050] The process for the production of alkali metal cyanide includes in particular i) the absorption of gaseous hydrogen cyanide, hydrogen cyanide-containing gas or liquid hydrogen cyanide into the aqueous alkali metal hydroxide solution to form an aqueous alkali metal cyanide solution in a container, ii) the crystallization of alkali metal cyanide from the alkali metal cyanide solution obtained in the container in an apparatus to form an aqueous alkali metal cyanide suspension, iii) the transport of the aqueous alkali metal cyanide solution through a first line from the container to the device, and iv) the transport of the aqueous alkali metal cyanide suspension from the device through a second line, wherein the first line and / or the second line is equipped with the system for online determination of one or more process parameters of the liquid transported through the line as described above.

[0051] The invention is further described by the following figure, which represents a preferred embodiment and is not intended to limit the invention in any way.

[0052] Fig.Figure 1 shows a schematic diagram of an exemplary embodiment of the system according to the invention. The system comprises a pipeline through which NaCN solution or NaCN suspension flows. A refractometer is located in the pipeline, which measures the refractive index and temperature of the NaCN solution or NaCN suspension online. From this, and taking into account the data transmitted by the ultrasonic device, the NaOH and NaCN content of the liquid can be determined. Downstream of the refractometer, an ultrasonic measuring device is located outside the pipeline. From the measured data of the ultrasonic measurement (in particular, flow velocity), and considering the data transmitted by the refractometer, the mass flow rate of the NaCN solution or NaCN suspension can be determined. Additionally, the ultrasonic measuring device can determine and output values ​​for density and temperature.Data is exchanged between the refractometer and the ultrasound measurement, which is necessary to determine the desired process parameters.

Claims

[1] Apparatus for carrying out a process for the production of alkali metal cyanide using gaseous hydrogen cyanide, hydrogen cyanide-containing gas or liquid hydrogen cyanide and an aqueous alkali metal hydroxide solution, comprising a) a conduit for transporting a liquid formed during the process, selected from an aqueous alkali metal cyanide solution or an aqueous alkali metal cyanide suspension and b) a system for online determination of one or more process parameters of the liquid transported through the pipeline, which serve for process control of the procedure, wherein the system comprises b1) a refractometer for measuring the refractive index of the liquid formed, wherein the refractometer or part thereof is arranged in the line for contact with the liquid, (b2) an ultrasonic measuring device for determining the mass flow rate of the liquid, wherein the ultrasonic measuring device is arranged outside the line without contact with the liquid, wherein the refractometer and the ultrasonic measuring device are configured to communicate with each other and exchange data, b3) one or more computing units configured to receive the readings from the refractometer and the ultrasonic measuring device, and the computing unit(s) configured to use the received readings from the refractometer and the ultrasonic measuring device to determine one or more process parameters of the liquid. [2] Apparatus according to claim 1, wherein one or more process parameters of the liquid to be determined are selected from the content of alkali metal hydroxide, the content of alkali metal cyanide, the mass flow rate, the density and the temperature, wherein the process parameters to be determined preferably include at least the content of alkali metal hydroxide and the content of alkali metal cyanide and particularly preferably all of the aforementioned process parameters. [3] Apparatus according to claim 1 or 2, wherein the one or more process parameters of the liquid to be determined include the alkali metal hydroxide content, the alkali metal cyanide content, the mass flow rate, the density and the temperature. [4] Apparatus according to one of the preceding claims, wherein a thermometer is integrated in the refractometer to measure the temperature of the liquid, and / or wherein separate data processing takes place in at least one computing unit assigned to the refractometer and in at least one computing unit assigned to the ultrasonic measuring device. [5] System according to one of the preceding claims, wherein the one or more computing units comprise a first computing unit and a second computing unit configured to exchange data with each other, wherein the first computing unit is associated with the refractometer and is configured to determine the alkali metal hydroxide content and the alkali metal cyanide content in the liquid using the measurements obtained from the refractometer and the ultrasonic measuring device, and the second computing unit is associated with the ultrasonic measuring device and is configured to determine the mass flow rate of the liquid using the measurements obtained from the refractometer and the ultrasonic measuring device. [6] System according to one of the preceding claims, wherein the ultrasonic measuring device is attached to the outside of the line. [7] Apparatus according to any of the preceding claims, wherein the alkali metal cyanide is sodium cyanide or potassium cyanide, wherein the alkali metal cyanide is preferably sodium cyanide. [8] Plant according to any one of the preceding claims, comprising i) a container for the absorption of gaseous hydrogen cyanide, hydrogen cyanide-containing gas or liquid hydrogen cyanide into the aqueous alkali metal hydroxide solution to form an aqueous alkali metal cyanide solution, ii) a device for crystallizing alkali metal cyanide from the alkali metal cyanide solution obtained in the container to form an aqueous alkali metal cyanide suspension, iii) a first conduit through which the aqueous alkali metal cyanide solution is transported from the container into the device, and iv) a second conduit through which the aqueous alkali metal cyanide suspension is transported from the apparatus, wherein the conduit for transporting the liquid formed during the process according to a) of claim 1 is the first conduit or the second conduit. [9] Plant according to claim 8, wherein the device for crystallization is an evaporative crystallizer that is heated and in which a vacuum is maintained, and / or The aqueous alkali metal cyanide suspension transported in the second line is subjected to solid-liquid separation to obtain solid alkali metal cyanide, which is preferably subjected to briquetting. [10] Plant according to one of the preceding claims, wherein the process control based on the determined process parameters comprises the control of the content of alkali metal hydroxide, particularly preferably the content of sodium hydroxide.

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