Urea solution preparation system and method

Abstract

The invention discloses a urea solution preparation system and method. The system comprises an ultrapure water preparation device used for preparing ultrapure water; the air energy heating device is used for heating the ultrapure water until the temperature reaches a set value; the feeding device is used for conveying urea particles to the stirring and dissolving tank; the stirring and dissolving tank is used for mixing and stirring the heated ultrapure water and urea particles into a urea solution; the urea solution filtering device comprises a precision filter and ultrafiltration equipment which are connected in sequence, and is used for filtering the urea solution; wherein the precision filter is used for intercepting fine particles and mechanical impurities and ensuring that the granularity of water entering the ultrafiltration equipment is less than 0.22 mu m, and the ultrafiltration equipment is used for further purifying suspended solids and impurities in a urea solution; the finished urea box is used for storing the filtered urea solution; and the automatic control system is used for controlling the operation of the whole system. According to the system, fine particles, impurities, suspended solids and the like are removed, and the crystallization risk is reduced.

Description

Technical Field

[0001] The invention relates to the field of environmentally friendly land-based power stations, environmentally friendly ships or denitrification technology, and in particular to a urea solution preparation system and method. Background Art

[0002] In order to meet the IMO emission regulations, ships are often equipped with a selective catalytic reduction denitrification system to reduce NOx emissions from diesel engine exhaust. Selective catalytic reduction denitrification is a process that uses NH 3 Convert NOx in flue gas into nitrogen and water. Liquid ammonia, ammonia water and urea can all be used as flue gas denitrification reducing agents. The method of choosing urea aqueous solution as the reducing agent for denitrification reaction is one of the most popular denitrification methods nowadays because it is safe and reliable. Purchasing finished urea solution is currently the main source of reducing agent for ship SCR system. The procurement cost is high and it is impossible to purchase and replenish it in time during the voyage of the ship, resulting in high procurement cost, labor cost and time cost.

[0003] In addition, we also found that in the current land-based power station, the dissolution of urea granules requires manual addition of materials during the preparation of urea solution, which takes up a lot of human resources and is time-consuming and labor-intensive. Due to the non-standard operation of personnel, the urea granules are not completely dissolved, the amount of urea solution is uncontrollable, and the liquid level of the urea dissolution tank is unstable, which makes it difficult to achieve stable and automatic operation of the system; after the urea solution is prepared, the urea granules and solution residues are prone to crystallization and clogging of pipelines. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, embodiments of the present application provide a urea solution preparation system and a control method thereof.

[0005] In order to achieve the above objectives, the technical solutions adopted in the embodiments of the present application are as follows:

[0006] In a first aspect, the present invention provides a urea solution preparation system, comprising:

[0007] Ultrapure water preparation device, used for preparing ultrapure water;

[0008] An air energy heating device, used to heat the ultrapure water until the temperature reaches a set value;

[0009] A feeding device, used to convey urea granules to the stirring and dissolving tank;

[0010] A stirring and dissolving tank is used to mix and stir the heated ultrapure water and urea granules into a urea solution;

[0011] A urea solution filtering device, comprising a precision filter and an ultrafiltration device connected in sequence, for filtering the urea solution; wherein the precision filter is used to intercept fine particles and mechanical impurities to ensure that the particle size of water entering the ultrafiltration device is less than 0.22 μm, and the ultrafiltration device is used to further purify suspended matter and impurities in the urea solution;

[0012] Finished urea tank is used to store filtered urea solution.

[0013] Furthermore, the ultrapure water preparation device adopts two-stage reverse osmosis combined with EDI process.

[0014] Furthermore, the air energy heating device adopts intelligent constant temperature control to heat the ultrapure water until the temperature reaches a set value of 35-60° C. Such control makes the temperature of the ultrapure water entering the dissolving and stirring device be 35-60° C., wherein the highest temperature of the ultrapure water in the dissolving and stirring device can reach 55-60° C., and is usually set to 40° C.

[0015] Furthermore, the precision filter of the urea solution filtering device is equipped with a polypropylene filter element. Furthermore, the precision filter adopts a multi-stage filter element structure including 5μm and 0.22μm filter elements.

[0016] Furthermore, the ultrapure water preparation device includes a tap water tank, a sand filter, an activated carbon filter, a scale inhibitor device, a 5μm fine filter, a primary RO system, a PH regulating pump, a secondary RO system, a RO pure water tank, an EDI system and an EDI pure water tank which are connected in sequence.

[0017] Furthermore, the urea solution preparation system also includes an automatic control system, which obtains a urea dissolution signal, including the amount of urea dissolved and the concentration of the urea solution, calculates the amount of ultrapure water required for the urea solution formulation, controls the delivery of ultrapure water from the EDI pure water tank to the stirring and dissolving tank, and judges and controls the delivery amount of ultrapure water according to the real-time liquid level value of the stirring and dissolving tank, and performs corresponding heating control according to the real-time temperature value in the EDI pure water tank.

[0018] Furthermore, the automatic control system also obtains the ultrapure water level value of the EDI pure water tank, and determines whether the ultrapure water level value is less than the minimum value of the EDI pure water tank. If so, a shutdown signal is generated to stop the ultrapure water delivery and start the ultrapure water preparation process until the ultrapure water level value is not less than the minimum value of the EDI pure water tank.

[0019] In a second aspect, the present invention provides a method for preparing a urea solution, comprising the following steps:

[0020] Acquire urea dissolution signals, including urea dissolution amount and urea solution concentration, and calculate the amount of ultrapure water required for urea solution formulation;

[0021] After confirming that the real-time temperature value in the EDI pure water tank is not less than the temperature setting value, a liquid inlet signal is generated to transport the ultrapure water in the EDI pure water tank to the stirring and dissolving tank; if the real-time temperature value is less than the temperature setting value, the liquid inlet pump is first turned off to heat the ultrapure water until the temperature reaches the setting value;

[0022] Obtain the real-time liquid level value of the stirring and dissolving tank, and determine whether the amount of ultrapure water added to the stirring and dissolving tank is not less than the amount of ultrapure water required for urea solution batching. If so, continue to deliver ultrapure water until the required amount is reached;

[0023] If the amount of ultrapure water is not less than the amount of ultrapure water required for the urea solution, a shutdown signal is generated to stop the ultrapure water delivery, and a loading signal is generated to deliver the urea granules to the stirring and dissolving tank, and the stirring device is started to mix the ultrapure water and urea granules into a urea solution;

[0024] The above urea solution is filtered to intercept fine particles and mechanical impurities to ensure that the water particle size entering the ultrafiltration equipment is less than 0.22μm, and then the suspended matter and impurities are removed.

[0025] Furthermore, the process of judging whether the amount of ultrapure water added to the stirring and dissolving tank is not less than the amount of ultrapure water required for the urea solution ingredients also includes the step of obtaining the ultrapure water level value of the EDI pure water tank, and judging whether the ultrapure water level value is less than the minimum value of the EDI pure water tank. If so, the ultrapure water delivery is stopped and the ultrapure water preparation process is started until the ultrapure water level value is not less than the minimum value of the EDI pure water tank.

[0026] Furthermore, the temperature setting value is 35-60°C; in the urea solution filtering step, the urea solution is filtered in sequence through a precision filter equipped with a polypropylene filter element and an ultrafiltration device, wherein the precision filter adopts a multi-stage filter element structure including 5μm and 0.22μm filter elements to ensure that the water particle size entering the ultrafiltration device is less than 0.22μm.

[0027] The present invention has the following beneficial effects:

[0028] The present invention uses an ultrapure water preparation device to prepare ultrapure water for dissolving urea granules and prepare the urea solution. The urea granules are placed in bags in a storage room, and after the bags are broken, they are transported to a stirring tank by an automatic feeder. The urea granules are dissolved into a urea solution of a required mass concentration by ultrapure water, and after passing through a precision filter and an ultrafiltration device, they are transported to a finished urea tank by a urea solution feed pump. The urea solution can be prepared at any time according to the use requirements, thereby solving the inconvenience of replenishing urea solution for ships at sea and reducing the procurement cost and operating cost of purchasing urea solution for denitration reaction. The whole set of equipment preferably adopts full automatic control, and can be manually / automatically controlled on site. Solve the problems of occupying a lot of human resources, time-consuming and labor-intensive, and high labor costs. The automatic control system is adopted to effectively realize the stable and automatic operation of the system, realize the complete dissolution of urea granules, the controllable amount of urea solution preparation, and the stable liquid level of the urea dissolution tank. After the urea solution is prepared, it is also finely filtered and ultrafiltered to remove the residual fine particles, impurities and suspended matter, etc., reduce the crystallization risk of the urea solution, and avoid crystallization blocking the pipeline. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention discloses a urea solution preparation system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings.

[0031] like Figure 1 As shown, the present invention discloses an embodiment of a urea solution preparation system, which uses an ultrapure water device to prepare ultrapure water for dissolving urea particles to prepare the urea solution.

[0032] The urea solution preparation system comprises an ultrapure water preparation device 1, an air energy heating device 2, a feeding device 3, a stirring and dissolving tank 4, a urea solution filtering device 5 and a finished urea tank 6. The urea solution filtering device 5 comprises a precision filter 51 and an ultrafiltration device 52. The ultrapure water preparation device (1) comprises a tap water tank 101, a sand filter 102, an activated carbon filter 103, an antiscalant device 104, a 5 μm fine filter 105, a primary RO system 106, a pH regulating pump 107, a secondary RO system 108, an RO pure water tank 109, an EDI system 110 and an EDI pure water tank 111 which are connected in sequence.

[0033] Urea granules are packed in bags and placed in a storage room. After the bags are broken, they are transported to a mixing tank by a feeding device (specifically, an automatic feeding machine). Ultrapure water is used to dissolve the urea granules into a urea solution of the required mass concentration. After passing through a precision filter 51 and an ultrafiltration device 52, the urea solution is transported to a finished urea tank 6 by a urea solution feeding pump.

[0034] The present invention designs an ultrapure water preparation device with a resistivity of more than 15 megohms, which can operate continuously. The water production per hour is 0.5 tons / hour, and the equipment process adopts the secondary reverse osmosis + EDI process;

[0035] (2) Use an air energy heating device to circulate and heat the ultrapure water in the EDI pure water tank. Using intelligent constant temperature control, the maximum water outlet temperature can reach 55℃ to 60℃. When the system is running, the heating temperature of the air energy heating device is usually set to 40℃;

[0036] The heated ultrapure water and urea granules are transported to the stirring and dissolving tank for homogenization and stirring to form a urea aqueous solution. The stirring and mixing time is about 30min-60min;

[0037] The urea solution filtering device 5 includes a precision filter and an ultrafiltration device. Among them, the main function of the precision filter 51 is to intercept fine particles, which is used to intercept a small amount of mechanical impurities leaked by the system. The precision filter cylinder is made of SUS304 material; 5 20-inch polypropylene filter elements are installed inside. The polypropylene filter element is a deep filter element with high efficiency and low resistance, which is suitable for further purification of water with low suspended impurities (turbidity less than 2-5 degrees). The polypropylene filter element is formed by polypropylene fibers wound on an injection-molded polypropylene porous tube according to a certain pattern to ensure that the particle size of water entering the ultrafiltration is less than 0.22um; when the pressure difference between the inlet and outlet water of the precision filter is greater than 1KG, the filter element in the filter needs to be replaced in time. The precision filter adopts a multi-stage filter element structure including 5μm and 0.22μm filter elements. Specifically, the precision filter includes a 5μm urea solution fine filter 511 and a 0.22μm urea solution fine filter 512.

[0038] The main function of the ultrafiltration device 52 is to improve the purity of the urea aqueous solution. After being stirred, the urea aqueous solution contains certain suspended matter and impurities, which need to be further purified. Therefore, after being filtered through a precision filter, it needs to be purified again.

[0039] The finished urea tank 6 is used to store the finished urea aqueous solution. The material is SUS304. The finished urea tank is equipped with a temperature transmitter and a liquid level transmitter with a 4-20mA liquid level signal; at the same time, the temperature and liquid level of the finished urea tank can also be transmitted to the touch screen and the selective catalytic reduction denitration control system.

[0040] Preferably, the urea solution preparation system also includes an automatic control system (not shown in the figure) to provide automatic control for the entire system and realize remote monitoring function. The main functions of the automatic control system are as follows:

[0041] i. The control system has three levels of management authority, with anti-fool and anti-misoperation settings. It will automatically log out and lock the screen after no operation for 5 minutes to prevent unauthorized personnel from entering the system to operate.

[0042] ii. The control system is standardized and reasonable, strong and weak electricity are separated, and the control circuit uses 24V safe voltage to reduce the risk of electric shock. It is safe and stable

[0043] iii. The equipment has overload, high voltage and low voltage protection. All faults and alarm systems are automatically recorded and saved. Each interface displays the current alarm record, making it easy to view the current alarm event.

[0044] In the event of a power failure, the operator's safety, equipment safety, and product safety are protected in turn. When the power is restored, the equipment will not start automatically and must be restarted by the operator before it can run automatically.

[0045] The present invention also provides a method for preparing a urea solution, comprising the following steps:

[0046] (1) obtaining a urea dissolution signal, including a urea dissolution amount and a urea solution concentration, and calculating an amount of ultrapure water required for urea solution formulation according to the urea dissolution amount and the urea solution concentration;

[0047] (2) After confirming that the real-time temperature value in the EDI pure water tank is not less than the temperature setting value, a liquid inlet signal is generated, and the 6# pump at the outlet of the EDI pure water tank is started to transport the ultrapure water in the EDI pure water tank to the stirring and dissolving tank; if the real-time temperature value is less than the temperature setting value, the 6# pump at the outlet of the EDI pure water tank is turned off, the air energy heating device is turned on, and the 5# pump (circulation pump) is turned on to circulate and heat the ultrapure water in the EDI pure water tank until the temperature reaches the setting value;

[0048] (3) Obtain the real-time liquid level value of the stirring and dissolving tank, and judge whether the amount of ultrapure water added to the stirring and dissolving tank is less than the amount of ultrapure water required for the urea solution formulation according to the real-time liquid level value. If it is less than, continue to deliver ultrapure water until the required amount is reached. If the amount of ultrapure water added to the stirring and dissolving tank is not less than the amount of ultrapure water required for the urea solution formulation, generate a shutdown signal, and in response to the shutdown signal, the 6# pump at the outlet of the EDI pure water tank stops running; at the same time, generate a feeding signal, and in response to the feeding signal, the feed switch valve of the urea dissolving tank is opened, and the urea granules are delivered to the stirring and dissolving tank, and the stirring device is started to mix and stir the ultrapure water and urea granules into a urea solution.

[0049] (4) Filter the urea solution, use a urea solution filter to intercept fine particles and mechanical impurities, ensure that the water particle size entering the ultrafiltration device is less than 0.22 μm, and then use the ultrafiltration device to remove suspended matter and impurities.

[0050] (5) In the process of determining whether the amount of ultrapure water added to the stirring and dissolving tank is not less than the amount of ultrapure water required for the urea solution formulation in step (3), it is also necessary to obtain the ultrapure water level value of the EDI pure water tank to determine whether the ultrapure water level value is less than the minimum value of the EDI pure water tank; if the ultrapure water level value is less than the minimum value of the EDI pure water tank, a shutdown signal is generated, and the 6# pump at the outlet of the EDI pure water tank stops running. At the same time, the ultrapure water preparation device is turned on to enter the ultrapure water preparation process until the ultrapure water level value is not less than the minimum value of the EDI pure water tank.

[0051] Furthermore, the temperature setting value is 35-60°C; in the urea solution filtering step, the urea solution is filtered in sequence through a precision filter equipped with a polypropylene filter element and an ultrafiltration device, wherein the precision filter adopts a multi-stage filter element structure including 5μm and 0.22μm filter elements to ensure that the water particle size entering the ultrafiltration device is less than 0.22μm.

[0052] The above-mentioned urea solution preparation system is used to prepare urea solution. Its process flow is mainly divided into four parts: ultrapure water preparation, heating and stirring, urea solution filtration, and terminal storage. The entire process is fully automatically controlled by an automatic control system, and can be manually / automatically controlled on site.

[0053] The process mainly includes:

[0054] (1) Ultrapure water preparation process: tap water → tap water tank → 1# pump → sand filter → activated carbon filter → antiscalant device → 5μm fine filter → 2# pump → primary RO system → 3# pump → PH regulating pump → secondary RO system → RO pure water tank → 4# pump → EDI system → EDI pure water tank;

[0055] (2) Urea solution preparation process: EDI pure water tank → 5# pump → air energy heating device → 6# pump → stirring system (including stirring and dissolving tank, feeding device) → 7# pump → 5μm urea solution fine filter → 0.22μm urea solution fine filter → ultrafiltration equipment → finished urea tank.

[0056] In the preparation process of ultrapure water, the treated water containing impurities can be recycled to improve water utilization, such as Figure 1 As shown, the concentrated water treated by the EDI system can be returned to the tap water tank; the concentrated water treated by the secondary RO system can be returned to the primary RO system. The designed output and recovery rate are as follows:

[0057] Serial number name Water output Remark 1 Ultrapure water production <![CDATA[0.5m 3 / h / set]]> Recovery rate: 65-70% 2 Single production volume of stirring dissolving tank <![CDATA[2.5m 3 / times]]> 3 Ultrafiltration equipment <![CDATA[4.0m 3 / h / set]]>

[0058] With the above-designed output and recovery rate, after the urea solution preparation system of the present invention is put into operation, the ultrapure water meets the following quality indicators:

[0059] Serial number name Water Quality Indicator name Detection method 1 Resistance Value ≧15MΩ / cm Resistance Value Instrument online detection

[0060] With the above-designed output and recovery rate, after the urea solution preparation system of the present invention is put into operation, the urea solution meets the following quality indicators:

[0061]

[0062]

Claims

1. A urea solution preparation system, characterized in that: include: Ultrapure water preparation device, used for preparing ultrapure water; An air energy heating device, used to heat the ultrapure water until the temperature reaches a set value; A feeding device, used to convey urea granules to the stirring and dissolving tank; A stirring and dissolving tank is used to mix and stir the heated ultrapure water and urea granules into a urea solution; A urea solution filtering device, comprising a precision filter and an ultrafiltration device connected in sequence, for filtering the urea solution; wherein the precision filter is used to intercept fine particles and mechanical impurities to ensure that the particle size of water entering the ultrafiltration device is less than 0.22 μm, and the ultrafiltration device is used to further purify suspended matter and impurities in the urea solution; Finished urea tank is used to store filtered urea solution.

2. The system according to claim 1, characterized in that The ultrapure water preparation device adopts two-stage reverse osmosis combined with EDI process.

3. The system according to claim 1, characterized in that: The air energy heating device adopts intelligent constant temperature control to heat the ultrapure water until the temperature reaches the set value of 35-60°C. Such control makes the temperature of the ultrapure water entering the dissolving and stirring device be 35-60°C, wherein the highest temperature of the ultrapure water in the dissolving and stirring device can reach 55-60°C, and is usually set to 40°C.

4. The system according to claim 1, characterized in that The precision filter of the urea solution filtering device is equipped with a polypropylene filter element. Furthermore, the precision filter adopts a multi-stage filter element structure including 5μm and 0.22μm filter elements.

5. The system according to claim 2, characterized in that The ultrapure water preparation device comprises a tap water tank, a sand filter, an activated carbon filter, a scale inhibitor device, a 5 μm fine filter, a primary RO system, a PH regulating pump, a secondary RO system, an RO pure water tank, an EDI system and an EDI pure water tank which are connected in sequence.

6. The system according to claim 5, characterized in that The urea solution preparation system also includes an automatic control system, which obtains a urea dissolution signal, including the amount of urea dissolved and the concentration of the urea solution, calculates the amount of ultrapure water required for urea solution formulation, controls the delivery of ultrapure water from the EDI pure water tank to the stirring and dissolving tank, and judges and controls the delivery amount of ultrapure water according to the real-time liquid level value of the stirring and dissolving tank, and performs corresponding heating control according to the real-time temperature value in the EDI pure water tank.

7. The system according to claim 6, characterized in that The automatic control system also obtains the ultrapure water level value of the EDI pure water tank, and determines whether the ultrapure water level value is less than the minimum value of the EDI pure water tank. If so, a shutdown signal is generated to stop the ultrapure water delivery and start the ultrapure water preparation process until the ultrapure water level value is not less than the minimum value of the EDI pure water tank.

8. A method for preparing a urea solution, characterized in that: The following steps are involved: Acquire urea dissolution signals, including urea dissolution amount and urea solution concentration, and calculate the amount of ultrapure water required for urea solution formulation; After confirming that the real-time temperature value in the EDI pure water tank is not less than the temperature setting value, a liquid inlet signal is generated to transport the ultrapure water in the EDI pure water tank to the stirring and dissolving tank; if the real-time temperature value is less than the temperature setting value, the liquid inlet pump is first turned off to heat the ultrapure water until the temperature reaches the setting value; Obtain the real-time liquid level value of the stirring and dissolving tank, and determine whether the amount of ultrapure water added to the stirring and dissolving tank is not less than the amount of ultrapure water required for urea solution batching. If so, continue to deliver ultrapure water until the required amount is reached; If the amount of ultrapure water is not less than the amount of ultrapure water required for the urea solution, a shutdown signal is generated to stop the ultrapure water delivery, and a loading signal is generated to deliver the urea granules to the stirring and dissolving tank, and the stirring device is started to mix the ultrapure water and urea granules into a urea solution; The above urea solution is filtered to intercept fine particles and mechanical impurities to ensure that the water particle size entering the ultrafiltration equipment is less than 0.22μm, and then the suspended matter and impurities are removed.

9. The method according to claim 8, characterized in that The process of judging whether the amount of ultrapure water added to the stirring and dissolving tank is not less than the amount of ultrapure water required for the urea solution ingredients also includes the step of obtaining the ultrapure water level value of the EDI pure water tank, and judging whether the ultrapure water level value is less than the minimum value of the EDI pure water tank. If so, the ultrapure water delivery is stopped and the ultrapure water preparation process is started until the ultrapure water level value is not less than the minimum value of the EDI pure water tank.

10. The method according to claim 8, characterized in that The temperature setting value is 35-60° C. In the urea solution filtering step, the urea solution is filtered in turn through a precision filter equipped with a polypropylene filter element and an ultrafiltration device, wherein the precision filter adopts a multi-stage filter element structure including 5 μm and 0.22 μm filter elements to ensure that the water particle size entering the ultrafiltration device is less than 0.22 μm.

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