阅读说明：本技术 一种食品级磷酸二氢钾制备工艺 (Preparation process of food-grade potassium dihydrogen phosphate ) 是由 拾佳 付勇 张俊 刘辉 赵强 于 2019-12-16 设计创作，主要内容包括：本发明公开一种食品级磷酸二氢钾制备工艺,将湿法磷酸制备得到的磷酸用于高纯磷酸二氢钾的制备,本发明提供的食品级磷酸二氢钾制备工艺,有效的降低了高纯磷酸二氢钾制备的成本,并具有工艺可控性高的优点,通过这一工艺可以生产得到符合食品级需求的高纯磷酸二氢钾晶体,而且晶体粒度分布均匀,细小粉末少；具有很高的市场价值。(The invention discloses a preparation process of food-grade monopotassium phosphate, wherein phosphoric acid prepared by wet-process phosphoric acid is used for preparing high-purity monopotassium phosphate; has high market value.)

1. A preparation process of food-grade monopotassium phosphate comprises the following steps:

feeding phosphoric acid and KOH solution into the neutralization reaction kettle (1) for neutralization reaction to obtain potassium dihydrogen phosphate solution;

cooling the potassium dihydrogen phosphate solution to 40-45 ℃ to obtain a potassium dihydrogen phosphate suspension;

separating the potassium dihydrogen phosphate suspension to obtain a liquid phase and a solid phase;

feeding the liquid phase into a concentration system for concentration and then feeding the liquid phase into the neutralization reaction kettle (1);

and drying the solid phase to obtain potassium dihydrogen phosphate crystals.

2. The process for preparing food grade monopotassium phosphate according to claim 1, wherein the step of reacting to obtain a potassium dihydrogen phosphate solution comprises:

heating phosphoric acid with the concentration of not less than 85% to 100-105 ℃;

and (2) feeding the heated phosphoric acid into a neutralization reaction kettle (1), continuously feeding a potassium hydroxide solution with the concentration of 48-50% into the neutralization reaction kettle (1) at a constant speed, and continuously stirring the neutralization reaction kettle (1) to fully react the phosphoric acid and the potassium hydroxide to obtain a potassium dihydrogen phosphate solution.

3. A process for preparing food grade monopotassium phosphate according to claim 2, wherein the step of obtaining monopotassium phosphate suspension comprises:

and (3) continuously stirring the potassium dihydrogen phosphate solution in the neutralization reaction kettle (1) to ensure that the temperature of the potassium dihydrogen phosphate solution in the neutralization reaction kettle (1) is reduced to 40-45 ℃ at the speed of 0.3-0.45 ℃/min to obtain a potassium dihydrogen phosphate suspension.

4. The preparation process of food grade monopotassium phosphate according to claim 2, characterized in that a stirring device is arranged in the neutralization reaction kettle (1), and at least two stages of stirring blades (13) are axially distributed on a stirring shaft of the stirring device.

5. The preparation process of food grade monopotassium phosphate according to claim 4, characterized in that the stirring device is connected with a variable frequency driving device (11), a temperature detection device (12) is arranged on the neutralization reaction kettle (1), the variable frequency driving device (11) is electrically connected with the temperature detection device (12), the temperature detection device (12) is used for detecting real-time temperature change of the neutralization solution in the neutralization reaction kettle (1), and the variable frequency driving device (11) is used for adjusting the stirring speed according to the detection result of the temperature detection device (12) to enable the temperature of the solution in the neutralization reaction kettle (1) to be 85-100 ℃.

6. A process for preparing food grade monopotassium phosphate according to claim 1, wherein the monopotassium phosphate suspension is separated into a liquid phase and a solid phase by a centrifuge (2), a steam pipeline (21) and a potassium hydroxide solution pipeline (22) are introduced into the centrifuge (2), the steam pipeline (21) is used for introducing saturated steam into the centrifuge (2), and the potassium hydroxide solution pipeline (22) is used for introducing a potassium hydroxide solution with the concentration of 48-50% into the centrifuge (2); the centrifuge (2) is also provided with a discharge pipeline (23).

7. A process for the preparation of food grade monopotassium phosphate according to claim 1, characterized in that said concentration system comprises a first evaporation chamber (41), a second evaporation chamber (42) and a third evaporation chamber (43); the shell side of the first evaporation chamber (41) is connected with a first steam pipeline, and the shell side of the second evaporation chamber (42) and the shell side of the third evaporation chamber (43) are connected with a second steam pipeline in series.

8. The preparation process of the food-grade monopotassium phosphate according to claim 7, wherein the liquid phase is sequentially heated and evaporated in the first evaporation chamber (41), the second evaporation chamber (42) and the third evaporation chamber (43), and the liquid phase with the density of 1.3-1.5 g/mL at normal temperature and normal pressure is concentrated into a mixed solution with the specific gravity of 1.5-1.55g/mL, 1.55-1.58g/mL and 1.58-1.63g/mL respectively.

9. The process for preparing food grade monopotassium phosphate according to claim 7, wherein the steam introduced through the first steam pipeline is used for heating the interior of the first evaporation chamber (41) to 100-110 ℃, the steam introduced through the second evaporation chamber (42) is used for heating the interior of the second evaporation chamber (42) to 80-90 ℃, and the steam introduced through the third evaporation chamber (43) is used for heating the interior of the third evaporation chamber (43) to 65-75 ℃.

10. A process for preparing food grade monopotassium phosphate according to claim 7, characterized in that the discharge ports of the first evaporation chamber (41), the second evaporation chamber (42) and the third evaporation chamber (43) are provided with a filtering device (44).

Technical Field

The invention relates to a preparation process of high-purity phosphate, in particular to a preparation process of food-grade monopotassium phosphate.

Background

Monopotassium phosphate is one of important products in the phosphate industry, and is widely applied to industries such as modern industry, food, medicine, agriculture and animal husbandry and the like. Among them, high-purity monopotassium phosphate is an important raw material for producing potassium metaphosphate, potassium pyrophosphate, other edible potassium salts and medical potassium salts. At present, the commonly used potassium dihydrogen phosphate preparation processes mainly include neutralization method, double decomposition method and the like.

The neutralization method generally utilizes a thermal phosphoric acid seat raw material and is prepared through neutralization reaction, but the method needs to use thermal phosphoric acid as a raw material, the thermal phosphoric acid has high requirement on phosphorite resources, although the prepared phosphoric acid has relatively high purity and relatively high cost, the neutralization reaction of the wet phosphoric acid widely used in China at present is not easy to control, other impurities are easy to introduce, the purity is reduced, and the use requirement of high-purity phosphate such as industrial-grade monopotassium phosphate and food-grade monopotassium phosphate cannot be met.

Disclosure of Invention

In order to solve the technical problems, the technical scheme provided by the invention provides a preparation process of food-grade potassium dihydrogen phosphate, which has the advantages of high process controllability and high phosphoric acid utilization rate, and potassium dihydrogen phosphate crystals meeting food-grade requirements can be produced and obtained through the process, and the crystals are uniform in particle size distribution and have high market value.

In view of the above, the present application discloses a process for preparing food-grade monopotassium phosphate, which comprises:

feeding phosphoric acid and KOH solution into the neutralization reaction kettle for neutralization reaction to obtain potassium dihydrogen phosphate solution;

cooling the potassium dihydrogen phosphate solution to 40-45 ℃ to obtain a potassium dihydrogen phosphate suspension;

separating the potassium dihydrogen phosphate suspension to obtain a liquid phase and a solid phase;

feeding the liquid phase into a concentration system for concentration and then feeding the liquid phase into the neutralization reaction kettle (1);

and drying the solid phase to obtain potassium dihydrogen phosphate crystals.

Preferably, the step of reacting to obtain the potassium dihydrogen phosphate solution comprises:

heating phosphoric acid with the concentration of not less than 85% to 100-105 ℃;

and (2) feeding the heated phosphoric acid into a neutralization reaction kettle (1), continuously feeding a potassium hydroxide solution with the concentration of 48-50% into the neutralization reaction kettle (1) at a constant speed, and continuously stirring the neutralization reaction kettle (1) to fully react the phosphoric acid and the potassium hydroxide to obtain a potassium dihydrogen phosphate solution.

Preferably, the step of obtaining a potassium dihydrogen phosphate suspension comprises:

and (3) continuously stirring the potassium dihydrogen phosphate solution in the neutralization reaction kettle (1) to ensure that the temperature of the potassium dihydrogen phosphate solution in the neutralization reaction kettle (1) is reduced to 40-45 ℃ at the speed of 0.3-0.45 ℃/min to obtain a potassium dihydrogen phosphate suspension.

Preferably, a stirring device is arranged in the neutralization reaction kettle (1), and at least two stages of stirring blades (13) are distributed on a stirring shaft of the stirring device along the axial direction.

Preferably, the stirring device is connected with a variable frequency driving device (11), a temperature detection device (12) is arranged on the neutralization reaction kettle (1), the variable frequency driving device (11) is electrically connected with the temperature detection device (12), the temperature detection device (12) is used for detecting the real-time temperature change of the neutralization solution in the neutralization reaction kettle (1), and the variable frequency driving device (11) is used for adjusting the stirring speed according to the detection result of the temperature detection device (12) so as to enable the temperature of the solution in the neutralization reaction kettle (1) to be 85-100 ℃.

Preferably, the potassium dihydrogen phosphate suspension is separated by a centrifuge (2) to obtain a liquid phase and a solid phase, a steam pipeline (21) and a potassium hydroxide solution pipeline (22) are introduced into the centrifuge (2), the steam pipeline (21) is used for introducing saturated steam into the centrifuge (2), and the potassium hydroxide solution pipeline (22) is used for introducing a potassium hydroxide solution with the concentration of 48-50% into the centrifuge (2); the centrifuge (2) is also provided with a discharge pipeline (23).

Preferably, the concentration system comprises a first evaporation chamber (41), a second evaporation chamber (42) and a third evaporation chamber (43); the shell side of the first evaporation chamber (41) is connected with a first steam pipeline, and the shell side of the second evaporation chamber (42) and the shell side of the third evaporation chamber (43) are connected with a second steam pipeline in series.

Preferably, the liquid phase is heated and evaporated in the first evaporation chamber (41), the second evaporation chamber (42) and the third evaporation chamber (43) in sequence, and the liquid phase with the density of 1.3-1.5 g/mL at normal temperature and normal pressure is concentrated into a mixed liquid with the specific gravity of 1.5-1.55g/mL, 1.55-1.58g/mL and 1.58-1.63g/mL respectively.

Preferably, the steam introduced by the first steam pipeline is used for heating the interior of the first evaporation chamber (41) to 100-110 ℃, the steam introduced by the second evaporation chamber (42) is used for heating the interior of the second evaporation chamber (42) to 80-90 ℃, and the steam introduced by the third evaporation chamber (43) is used for heating the interior of the third evaporation chamber (43) to 65-75 ℃.

Preferably, the discharge ports of the first evaporation chamber (41), the second evaporation chamber (42) and the third evaporation chamber (43) are provided with filtering devices.

Compared with the prior art, the detailed description of the application is as follows:

the application discloses a preparation process of food-grade phosphate, which can use wet-process phosphoric acid as a raw material, and realizes a process for preparing high-purity monopotassium phosphate by a wet-process phosphoric acid neutralization method through neutralization reaction with potassium hydroxide and by utilizing reaction heat and controlling cooling crystallization nodes.

Furthermore, the system preheats phosphoric acid, combines the reaction heat of phosphoric acid and potassium hydroxide reaction, makes potassium dihydrogen phosphate in the stirring process of reaction, and the concentration of potassium dihydrogen phosphate is less than the saturated solution concentration of potassium dihydrogen phosphate under this temperature all the time, makes in the neutralization reaction process not have the crystal to separate out all the time, the effectual crystal quality that has improved.

In addition, the process further controls the speed of cooling to precipitate crystals, the temperature change condition in the neutralization reaction kettle can be known according to the detection result of the temperature detection device in the cooling stage, the specific heat capacity of the potassium dihydrogen phosphate suspension is also continuously changed due to the existence of variables such as water volatilization, concentration change, crystallization density change and the like in the cooling crystallization process of the potassium dihydrogen phosphate solution, and the rotating speed of the variable frequency driving device is flexibly adjusted according to the temperature change condition, so that the potassium dihydrogen phosphate solution is cooled at a stable speed. The prepared crystal has good product appearance and meets the requirements of food-grade potassium dihydrogen phosphate on the control of crystal granularity and fine particles.

The utility model provides a first evaporating chamber and second evaporating chamber all directly let in the heat source steam that has a high temperature, can avoid because of the liquid phase evaporation rate that the liquid phase dilution leads to is slow, the problem of inefficiency, unable in time seeing off, have guaranteed the steady operation of system.

Drawings

FIG. 1 is a process flow diagram of the present application;

FIG. 2 is a flow diagram of a system employing the process of the present application.

Detailed Description

In order to make the technical solutions of the present invention better understood by those skilled in the art, the present invention will be further described in detail with reference to the accompanying drawings and specific embodiments.

As shown in the figure, the application discloses a preparation process of monopotassium phosphate, which comprises the following steps:

feeding phosphoric acid with the concentration not less than 85% and KOH solution into a neutralization reaction kettle (1) to obtain potassium dihydrogen phosphate solution;

cooling the potassium dihydrogen phosphate solution to 40-50 ℃ to obtain a potassium dihydrogen phosphate suspension;

conveying the potassium dihydrogen phosphate suspension into a centrifugal machine (2) for centrifugal separation to obtain a liquid phase and a solid phase, conveying the liquid phase into a concentration system, concentrating and adjusting the pH value of the liquid phase, and then conveying into the neutralization reaction kettle (1); the solid phase is sent into a fluidized bed (3) to be dried to obtain potassium dihydrogen phosphate crystals.

Wherein, the solid phase and the liquid phase are both understood to be a mixture containing a solid and a liquid, wherein the solid phase is a solid particulate mixed with a small amount of liquid; the liquid phase is a liquid mixed with a small amount of suspended monopotassium phosphate crystals.

The preparation process of the monopotassium phosphate disclosed by the application specifically comprises the following steps:

heating phosphoric acid with the concentration of not less than 85% to 100 ℃, feeding the heated phosphoric acid into a neutralization reaction kettle (1), continuously feeding a potassium hydroxide solution with the concentration of 48-50% into the neutralization reaction kettle (1) at a constant speed, and continuously stirring the neutralization reaction kettle (1) to fully reflect the phosphoric acid and the potassium hydroxide to obtain a potassium dihydrogen phosphate solution;

continuously stirring the potassium dihydrogen phosphate solution in the neutralization reaction kettle (1) to cool the potassium dihydrogen phosphate solution to 40-45 ℃ to obtain a potassium dihydrogen phosphate suspension;

conveying the potassium dihydrogen phosphate suspension into a centrifugal machine (2) for centrifugal separation to obtain a liquid phase and a solid phase;

the solid phase is sent into a fluidized bed (3) through a material distribution device, and the fluidized bed (3) is used for drying the solid phase to prepare potassium dihydrogen phosphate crystals;

and (3) feeding the liquid phase into a concentration system, concentrating the liquid phase into a saturated solution, adjusting the pH value of the liquid phase, and feeding the liquid phase into a neutralization reaction kettle (1).

Neutralization reaction cauldron (1) in reaction process, through preheating phosphoric acid, improved the solubility of potassium dihydrogen phosphate in aqueous, combine the reaction heat of phosphoric acid and potassium hydroxide reaction for potassium dihydrogen phosphate is in the stirring in-process of reaction, and the concentration of potassium dihydrogen phosphate is less than the saturated solution concentration of potassium dihydrogen phosphate under this temperature all the time. Because the potassium dihydrogen phosphate solubility that excessive stirring heat dissipation leads to reduces excessively fast need be avoided, be provided with the agitating unit that can the variable speed regulation in the neutralization reaction cauldron (1) of this application.

The stirring device comprises a stirring shaft, the stirring shaft is connected with a variable frequency driving device (11), and a plurality of stages of stirring blades (13) are arranged on the stirring shaft along the axial direction.

Stirring vane (13) are multistage stirring vane (13), can stir liquid at the different liquid level degree of depth in neutralization reation kettle (1), guarantee that the reaction is effective, abundant, if lead to local monopotassium phosphate concentration too high because of not fully stirring, or local unbalanced reaction heat leads to the temperature to descend, can cause neutralization reation kettle (1) internal product to form the suspension crystallization, and these crystallization can destroy the crystal form of monopotassium phosphate, reduce product quality.

In addition, the frequency conversion driving device (11) of this application is connected with controlling means be provided with temperature-detecting device (12) on neutralization reaction cauldron (1), temperature-detecting device (12) are used for detecting the real-time temperature variation of neutralization liquid in neutralization reaction cauldron (1), frequency conversion driving device (11) are used for adjusting the stirring speed according to the testing result of temperature-detecting device (12), and then adjust the temperature variation condition of neutralization liquid in neutralization reaction cauldron (1), guarantee that temperature keeps 85-100 ℃ in neutralization reaction cauldron (1). According to the temperature change condition, such as real-time temperature parameters, the variable-frequency driving device (11) can adjust the rotating speed, reduce the heat loss caused by the stirring device in the neutralization reaction kettle (1), and keep the temperature in the reaction kettle at 85-100 ℃.

At the temperature, the potassium dihydrogen phosphate has higher solubility in the neutralization reaction kettle (1), and the potassium dihydrogen phosphate generated by the neutralization reaction is ensured to be effectively dissolved in an unsaturated state all the time.

When the neutralization reaction kettle (1) needs to stop reacting, stopping introducing the phosphoric acid and the potassium hydroxide, continuously stirring the potassium dihydrogen phosphate solution in the neutralization reaction kettle (1), continuously stirring the potassium dihydrogen phosphate solution at the rotating speed of 120-148r/min, cooling the potassium dihydrogen phosphate solution in the reaction kettle at the speed of 0.3-0.45 ℃/min, and stopping stirring until the temperature of the potassium dihydrogen phosphate solution is reduced to 40-45 ℃ to obtain the potassium dihydrogen phosphate suspension. At this time, as the potassium dihydrogen phosphate solution is cooled, crystals with reduced solubility are precipitated, and a potassium dihydrogen phosphate suspension is formed. At this stirring speed, crystals can be effectively and uniformly dispersed in the suspension, and as the saturation degree of the potassium dihydrogen phosphate decreases, the potassium dihydrogen phosphate suspension with good crystal morphology distribution can be formed.

In the cooling and crystal growing stage, the temperature change condition in the neutralization reaction kettle (1) can be known according to the detection result of the temperature detection device (12), the specific heat capacity of the monopotassium phosphate suspension is continuously changed due to the existence of variables such as water volatilization, concentration change, crystal density change and the like in the cooling and crystallization process of the monopotassium phosphate solution, and the rotating speed of the variable frequency driving device (11) is flexibly adjusted according to the temperature change condition, so that the monopotassium phosphate solution can be cooled at the speed of 0.3-0.45 ℃/min all the time. The crystal generated by the process is analyzed through experiments, the granularity of 90% of the crystal of the monopotassium phosphate formed by the process is 1.5-1.8mm, the product has good appearance, and the requirements of food-grade monopotassium phosphate on the control of the granularity of the crystal and fine particles are met.

And (3) sending the potassium dihydrogen phosphate suspension into a centrifuge (2) for separation to obtain a solid phase and a liquid phase, sending the solid phase out to a fluidized bed (3), and sending the liquid phase to a concentration system.

The centrifugal machine (2) is internally provided with a steam pipeline (21) and a potassium hydroxide solution pipeline (22), the centrifugal machine (2) is also provided with a discharge pipeline (23), and the discharge pipeline (23) is connected to a concentration system.

The steam pipeline (21) is used for introducing saturated steam into the centrifuge (2), the saturated steam heats the accumulated material in the centrifuge (2), and the saturated steam is liquefied when meeting the cold and improves the solubility of the accumulated material in water, so that the effect of cleaning the centrifuge (2) is realized. In addition, the potassium hydroxide solution pipeline (22) is used for introducing a potassium hydroxide solution into the centrifugal machine (2), the potassium hydroxide solution is matched with the steam heating effect, the acid accumulated materials which are not easy to dissolve in the centrifugal machine (2) can be dissolved, and the cleaned liquid is sent to a concentration system through a discharge pipeline (23) for recycling.

The top of fluidized bed (3) is provided with vibrations distributing device (31), vibrations distributing device (31) are provided with the vibrations unloading of shock dynamo in order to realize the distributing device, because the solid phase that this application let in fluidized bed (3) is the moist crystallization mixture that contains a small amount of liquid, and mobility is relatively poor, and it is inhomogeneous or local fluidization recrystallization to lead to the part to be heated in order to avoid the material to pile up, consequently realizes even cloth through vibrations distributing device (31).

And introducing the liquid phase into a concentration system, and heating and concentrating the liquid phase through steam. In addition, the cleaning liquid delivered by the centrifuge (2) through the discharge line (23) is also passed into the concentration system, mixed with the liquid phase and concentrated by steam heating.

The concentration system comprises a first evaporation chamber (41), a second evaporation chamber (42) and a third evaporation chamber (43); the shell side of the first evaporation chamber (41) is connected with a first steam pipeline, and the shell side of the second evaporation chamber (42) and the shell side of the third evaporation chamber (43) are connected with a second steam pipeline in series. Specifically, a second steam inlet and a second steam outlet are arranged in the second evaporation chamber (42), the second steam outlet is connected to a third steam inlet of the third evaporation chamber (43), a second steam pipeline is fed through the second steam inlet, and the second evaporation chamber (42) and the third evaporation chamber (43) are heated and concentrated in sequence.

The steam introduced by the first steam pipeline is used for heating the interior of the first evaporation chamber (41) to 100-110 ℃, the steam introduced by the second evaporation chamber (42) heats the interior of the second evaporation chamber (42) to 80-90 ℃, and the recovery steam introduced by the third evaporation chamber (43) heats the third evaporation chamber (43) to 65-75 ℃. The liquid phase is sequentially heated and evaporated in the first evaporation chamber (41), the second evaporation chamber (42) and the third evaporation chamber (43), and the liquid phase with the density of 1.3-1.5 g/mL at normal temperature and normal pressure is concentrated into mixed liquid with the specific gravity of 1.5-1.55g/mL, 1.55-1.58g/mL and 1.58-1.63g/mL respectively. Through the concentration system, water in the liquid phase is evaporated, impurities are removed, and then the liquid phase is sent back to the neutralization reaction kettle (1).

Heat source steam is directly introduced into the first evaporation chamber (41) and the second evaporation chamber (42), the steam temperature is higher than the liquid phase boiling temperature, so that the liquid phases in the first evaporation chamber (41) and the second evaporation chamber (42) are always in a boiling state, moisture in the liquid phases is quickly volatilized in the boiling state, the liquid phases are quickly concentrated, and the liquid phase recycling efficiency is improved; in addition, because in this application, recycled centrifuge (2) interior because of saturated steam or potassium hydroxide solution, lead to the liquid phase in first evaporating chamber (41) to be further diluted by the water in the water and the potassium hydroxide solution that steam liquefaction formed, first evaporating chamber (41) and second evaporating chamber (42) of this application all directly let in the heat source steam that has a high temperature, can avoid because of the liquid phase evaporation rate that the liquid phase dilution leads to is slow, inefficiency, the problem that can't in time send out, the steady operation of system has been guaranteed.

And a pH value detection device and a phosphoric acid titration device are further arranged in the first evaporation chamber (41), the second evaporation chamber (42) and the third evaporation chamber (43), the phosphoric acid titration device is used for introducing excessive phosphoric acid into the evaporation chambers, and the pH detection device is used for determining the end point of the pH value of the liquid phase adjusted by the third evaporation chamber (43) so that the pH value of the liquid phase is between 4 and 4.2.

The third evaporation chamber (43) is connected with the neutralization reaction kettle (1). And the discharge ports of the first evaporation chamber (41), the second evaporation chamber (42) and the third evaporation chamber (43) are respectively provided with a filtering device (44), and the filtering devices (44) are used for removing colloidal precipitates generated in the concentration boiling process of the liquid phase, such as MgHPO4, CaHPO4 and the like. After the colloidal precipitates are filtered, the cationic impurities accumulated in the process are further reduced, the purity of the product is improved, and the impurity enrichment caused by liquid phase circulation is avoided.

Analyzing the components or element contents of monopotassium phosphate prepared by a filtered liquid phase of a concentration system and monopotassium phosphate prepared by an unfiltered liquid phase of the concentration system respectively to obtain the following main components in percentage by mass:

in addition, fluidized bed (3) are dry back and are sent out the monopotassium phosphate crystal through the lifting hopper to send to the feed bin through the distributing device be provided with electro-magnet (5) in the distributing device, electro-magnet (5) are arranged in getting rid of the material in the magnetic metal powder of whole system inevitable interfusion, further promote the quality of product.

The above is only a preferred embodiment of the present invention, and it should be noted that the above preferred embodiment should not be considered as limiting the present invention, and the protection scope of the present invention should be subject to the scope defined by the claims. It will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the spirit and scope of the invention, and these modifications and adaptations should be considered within the scope of the invention.