Organic fertilizer and preparation method thereof

Abstract

The invention discloses an organic fertilizer and a preparation method thereof, and belongs to the technical field of fertilizer production. The organic fertilizer provided by the invention is prepared from the following raw materials in parts by weight: 4-6 parts of cow dung, 0.5-1.5 parts of straws and desulfurized gypsum accounting for 5-13% of the total weight of the cow dung and the straws through a method of sealed fermentation and forced aeration. A large amount of SO4 < 2-> contained in the desulfurized gypsum can react with NH3 to generate (NH4) 2SO4 in the composting fermentation process, NH3 volatilization and nitrogen loss can be effectively reduced, the purposes of reducing the pH of the organic fertilizer and reducing the nitrogen loss are achieved, and on the other hand, resource utilization of the desulfurized gypsum and solid waste of agriculture and animal husbandry can be promoted.

Description

Technical Field

[0001] The invention belongs to the technical field of fertilizer production, and in particular relates to an organic fertilizer and a preparation method thereof. Background Art

[0002] In recent years, the development and application of sulfur-rich and calcium-rich organic fertilizers have gradually become the focus of agricultural research. According to the needs of plant nutrition, researchers have adopted a variety of approaches to enhance the efficiency of fertilizers. Among them, by adjusting the ratio of sulfur and calcium components in fertilizers, it can not only promote plant growth, but also improve soil structure. In the traditional fertilizer preparation process, adding sulfur and calcium components is an effective means to improve fertilizer efficiency, which is not only conducive to adjusting the soil pH value, but also provides the sulfur and calcium nutrients required by plants. At the same time, the release of nitrogen in the form of ammonia during the composting process limits the quality of the compost, resulting in a decrease in compost nutrition.

[0003] Desulfurized gypsum, also known as flue gas desulfurization gypsum, is a solid waste generated by coal-fired power plants or other industrial facilities when using wet flue gas desulfurization technology to treat sulfur-containing flue gas. It is mainly produced by reacting sulfur dioxide (SO2) in the flue gas with calcium-based substances in limestone slurry to produce calcium sulfate (CaSO4·2H2O), commonly known as gypsum. With the increasingly stringent environmental regulations, more and more power plants have begun to install flue gas desulfurization systems, resulting in a huge amount of desulfurized gypsum. Its resource utilization not only helps to reduce environmental pressure, but also brings economic benefits to enterprises. Therefore, it is urgent to develop a fertilizer preparation method that can utilize desulfurized gypsum, increase the S and Ca content of compost products, reduce nitrogen loss, and adjust the pH value of compost. Summary of the invention

[0004] In view of the deficiencies in the prior art, the object of the present invention is to provide an organic fertilizer and a preparation method thereof, so as to solve the problems of large nitrogen loss in composting materials and low utilization rate of desulfurized gypsum in the prior art.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: an organic fertilizer is provided, comprising the following raw materials in parts by weight: 4-6 parts of cow dung, 0.5-1.5 parts of straw, and 5-13% of the total weight of cow dung and straw in desulfurized gypsum.

[0006] The invention has the following beneficial effects: cow dung is the main nitrogen source in the composting process, and it contains rich organic matter, which can provide necessary nutrition for composting and promote the growth and reproduction of microorganisms. At the same time, cow dung itself also contains a large number of microorganisms; straw is rich in cellulose and hemicellulose, and is the main carbon source in composting. Its good structure helps to increase the air permeability of composting and improve the ventilation performance of composting; the main component of desulfurized gypsum is CaSO4·2H2O, which can effectively adjust the pH value of organic fertilizer in composting and increase the content of calcium and sulfur in composting products. Cow dung provides rich macro elements such as nitrogen, phosphorus, potassium, etc., while desulfurized gypsum provides calcium and sulfur. The combination of the two makes the nutritional components of organic fertilizer more comprehensive, meets the needs of crops for multiple elements, and promotes the overall growth of plants.

[0007] On the basis of the above technical solution, the present invention can also be improved as follows:

[0008] Furthermore, the method comprises the following raw materials in parts by weight: 5 parts of cow dung, 1 part of straw, and desulfurized gypsum accounting for 10% of the total weight of the cow dung and the straw.

[0009] The present invention also provides a method for preparing the above organic fertilizer, comprising the following steps:

[0010] S1. Raw material processing: crushing the straw to obtain straw powder, mixing the cow dung, straw powder and desulfurized gypsum to obtain a mixed material;

[0011] S2. Composting fermentation: The moisture content of the mixed material is adjusted to 55-65%, and then filled into the composting device for sealed fermentation;

[0012] S3. Aeration: Force aeration is performed on the mixed materials in the composting device every day, with an aeration rate of 0.7-1.0 L / min / kg of mixed materials. Aeration is performed once every two hours from 0 to 8 o'clock, and once every hour at other times. Each aeration time is 3-8 minutes.

[0013] S4. Turning the pile: Turn the pile during the composting process and ferment the compost for 40 to 45 days to obtain organic fertilizer.

[0014] Furthermore, the particle size of the straw powder is 2 to 5 cm.

[0015] Furthermore, the aeration volume was 0.88 L / min / kg of mixed material, and each aeration time was 5 min.

[0016] Furthermore, the time for turning the compost is 0th, 3rd, 7th, 14th, 21st, 28th, 35th and 42nd day from the start of composting, and the composting fermentation time is 42 days.

[0017] Furthermore, the composting device includes a barrel body 1 and a barrel cover 2. An aeration hole 4 is provided at the lower side wall of the barrel body 1, and the aeration hole 4 is connected to the aeration device 3 through a second ventilation pipe 10; the barrel cover 2 is provided with a temperature measuring hole 5 and a three-way valve 6, one end of the three-way valve 6 is connected to the greenhouse gas collection device 7, and the other end is connected to the ammonia absorption device 9 through a first ventilation pipe 8.

[0018] Furthermore, the barrel body 1 and the barrel cover 2 are made of stainless steel.

[0019] Furthermore, the ammonia absorption device 9 is filled with a boric acid solution and an indicator.

[0020] The present invention has the following beneficial effects: the present invention uses desulfurized gypsum as an additive for composting, and the large amount of SO4 contained in the desulfurized gypsum 2- It can react with NH3 to generate (NH4)2SO4 during the composting fermentation process. On the one hand, it can increase the S and Ca nutrient content of the compost product, reduce nitrogen loss, and adjust the pH value of the compost. On the other hand, it can also promote the resource utilization of desulfurized gypsum and agricultural and animal husbandry solid waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a structural diagram of a composting device according to Embodiment 1 of the present invention;

[0022] Among them, 1. barrel body; 2. barrel cover; 3. aeration device; 4. aeration hole; 5. temperature measuring hole; 6. three-way valve; 7. greenhouse gas collection device; 8. first ventilation pipe; 9. ammonia absorption device; 10. second ventilation pipe;

[0023] Figure 2 The figure is a trend chart of the daily gas emission during the composting process of Examples 2-3 and Comparative Example 1, wherein a is the daily emission of NH3, b is the daily emission of CO2, c is the daily emission of N2O, and d is the daily emission of CH4;

[0024] Figure 3 It is a pH variation trend diagram of the organic fertilizer samples of Examples 2-3 and Comparative Example 1 during the composting process;

[0025] Figure 4 The graph is a trend chart of organic matter (%), total nitrogen (%) and C / N changes of the organic fertilizer samples of Examples 2-3 and Comparative Example 1 during the composting process, wherein a is organic matter, b is total nitrogen, and c is C / N. DETAILED DESCRIPTION

[0026] The principles and features of the present invention are described below in conjunction with the examples, which are only used to explain the present invention and are not intended to limit the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0027] Embodiment 1:

[0028] An organic fertilizer composting device, such as Figure 1 As shown, it includes a barrel body 1 and a barrel cover 2. An aeration hole 4 is provided at the lower side wall of the barrel body 1, and the aeration hole 4 is connected to the aeration device 3 through a second ventilation pipe 10 with a valve; the barrel cover 2 is provided with a temperature measuring hole 5 and a three-way valve 6, and the temperature measuring hole 5 is equipped with a plugging core. One end of the three-way valve 6 is connected to the greenhouse gas collection device 7, and the other end is connected to the ammonia absorption device 9 through a first ventilation pipe 8 with a valve; the barrel body 1 is a cylinder with a diameter of 40 cm, a height of 60 cm, and a volume of 70 L, and is preferably made of stainless steel.

[0029] During the composting process, the barrel cover 2 is opened, the compost material is filled into the barrel, and then the barrel cover 2 is closed for composting fermentation. During the composting process, the aeration device 3 is used for forced aeration, and the gas enters the bottom of the barrel body 1 through the second ventilation pipe 10, which can effectively control the temperature, humidity and oxygen concentration inside the pile body, provide optimal conditions for the growth and metabolic activities of microorganisms, maintain the aerobic state of the pile body, and improve the composting efficiency; the ammonia absorption device 9 is a conical flask, which is filled with boric acid solution and an indicator (methyl red bromocresol green mixed solution indicator, which is titrated by color change to quantitatively analyze the amount of ammonia produced). The ammonia generated during the composting fermentation process enters the ammonia absorption device through the three-way valve 6 and the first ventilation pipe 8, and is absorbed by the boric acid solution. The greenhouse gases (N2O, CH4 and CO2) generated during the composting process enter the greenhouse gas collection device 7 through the three-way valve 6; during the composting fermentation process, the temperature measuring device can be inserted into the temperature measuring hole 5 to monitor the pile body temperature in real time.

[0030] Embodiment 2:

[0031] An organic fertilizer (FGDG5%) comprises the following raw materials in parts by weight: 5 parts of fresh cow dung, 1 part of wheat straw, and 5% of desulfurized gypsum in the total weight of the fresh cow dung and the straw.

[0032] The preparation method of the above-mentioned organic fertilizer comprises the following steps:

[0033] S1. Raw material processing: crush wheat straw into 3 cm powder segments, collect fresh cow dung from a cattle farm, and fully mix the fresh cow dung, straw powder segments and desulfurized gypsum to obtain a mixed material;

[0034] S2. Composting fermentation: The moisture content of the mixture is adjusted to about 60% by drying or adding water, and then filled into the composting device described in Example 1 and sealed for fermentation;

[0035] S3. Aeration: The mixed materials in the composting device are forced to be aerated every day, with an aeration rate of 0.88L / min / kg of mixed materials, aeration once every two hours from 0 to 8 o'clock, and once every hour at other times, and each aeration time is 5min;

[0036] S4. Turning the compost: Turn the compost thoroughly on the 0th, 3rd, 7th, 14th, 21st, 28th, 35th and 42nd day from the start of composting. After turning, keep the original spatial properties and continue fermentation. Fermentation is completed after 42 days of composting.

[0037] Embodiment 3:

[0038] An organic fertilizer (FGDG 10%) comprises the following raw materials in parts by weight: 5 parts of fresh cow dung, 1 part of wheat straw, and desulfurized gypsum accounting for 10% of the total weight of the fresh cow dung and the straw.

[0039] The preparation method of the above-mentioned organic fertilizer comprises the following steps:

[0040] S1. Raw material processing: crush wheat straw into 3 cm powder segments, collect fresh cow dung from a cattle farm, and fully mix the fresh cow dung, straw powder segments and desulfurized gypsum to obtain a mixed material;

[0041] S2. Composting fermentation: The moisture content of the mixture is adjusted to about 60% by drying or adding water, and then filled into the composting device described in Example 1 and sealed for fermentation;

[0042] S3. Aeration: The mixed materials in the composting device are forced to be aerated every day, with an aeration rate of 0.88L / min / kg of mixed materials, aeration once every two hours from 0 to 8 o'clock, and once every hour at other times, and each aeration time is 5min;

[0043] S4. Turning the compost: Turn the compost thoroughly on the 0th, 3rd, 7th, 14th, 21st, 28th, 35th and 42nd day from the start of composting. After turning, keep the original spatial properties and continue fermentation. Fermentation is completed after 42 days of composting.

[0044] Comparative Example 1:

[0045] An organic fertilizer (CK) comprises the following raw materials in parts by weight: 5 parts of fresh cow dung and 1 part of wheat straw.

[0046] The preparation method of the above-mentioned organic fertilizer comprises the following steps:

[0047] S1. Raw material processing: crush wheat straw into 3 cm powder segments, collect fresh cow dung from a cattle farm, and fully mix the fresh cow dung and straw powder to obtain a mixed material;

[0048] S2. Composting fermentation: The moisture content of the mixture is adjusted to about 60% by drying or adding water, and then filled into the composting device described in Example 1 and sealed for fermentation;

[0049] S3. Aeration: The mixed materials in the composting device are forced to be aerated every day, with an aeration rate of 0.88L / min / kg of mixed materials, aeration once every two hours from 0 to 8 o'clock, and once every hour at other times, and each aeration time is 5min;

[0050] S4. Turning the compost: Turn the compost thoroughly on the 0th, 3rd, 7th, 14th, 21st, 28th, 35th and 42nd day from the start of composting. After turning, keep the original spatial properties and continue fermentation. Fermentation is completed after 42 days of composting.

[0051] Experimental example:

[0052] The organic fertilizers prepared in Examples 2-3 and Comparative Example 1 were tested and analyzed for their performance effects.

[0053] 1. Ammonia and greenhouse gas emissions

[0054] The syringe was used as the greenhouse gas collection device 7. During the composting process, CO2, CH4 and N2O were collected by the syringe collection method every morning, and their emissions were detected by gas chromatography. The boric acid solution that absorbed ammonia in the ammonia absorption device 9 was titrated to detect the amount of NH3 (ammonia) produced. The specific experimental results are shown in Table 1:

[0055] Table 1 Cumulative emissions of gases from different treatments

[0056] Experimental groups <![CDATA[NH3(g)]]> <![CDATA[N2O(g)]]> <![CDATA[CO2(kg)]]> <![CDATA[CH4(g)]]> CK 2.18 0.33 1.24 0.83 FGDG5% 0.55 6.65 1.53 0.62 FGDG10% 0.32 0.41 0.93 0.67

[0057] Figure 2 The following is a trend chart of daily gas emissions during the composting process (among which, a-NH3 daily emissions, b-CO2 daily emissions, c-N2O daily emissions, d-CH4 daily emissions). It can be seen from the figure that after adding 5% desulfurized gypsum, the daily emissions of ammonia (NH3) and methane (CH4) in the compost decreased compared with the CK treatment group. The daily emissions of nitrous oxide (N2O) were significantly higher than those of the CK treatment group in the later stage of composting (after 16 days). The daily emissions of carbon dioxide (CO2) were lower than those of the CK treatment group during the warming period (1 to 3 days), and then exceeded those of the CK treatment group, and were higher than those of the FGDG10% treatment group. After adding 10% desulfurized gypsum, the daily emissions of ammonia (NH3), carbon dioxide (CO2), and methane (CH4) in the compost decreased compared with the CK treatment group. The most significant emission rate was that of NH3. This is because the gypsum contains a large amount of SO4 2-It can react with NH3 to generate (NH4)2SO4 during the composting fermentation process, which can effectively reduce the volatilization of NH3; the daily emission of nitrous oxide (N2O) is sometimes higher than that of the CK treatment group. Combined with Table 2, it can be seen that after adding 5% desulfurized gypsum, the nitrogen loss in the form of ammonia (NH3) decreased by 74.77%, the nitrogen loss in the form of nitrous oxide (N2O) increased by more than 19 times, the carbon loss in the form of CO2 increased by 23.39%, and the loss in the form of CH4 decreased by 25.30%. After adding 10% desulfurized gypsum, the nitrogen loss in the form of ammonia (NH3) decreased by 85.17%, the nitrogen loss in the form of nitrous oxide (N2O) increased by 24.24%, and the carbon loss in the form of CO2 and CH4 decreased by 24.99% and 19.28%, respectively. It can be clearly seen that with the increase in the amount of desulfurized gypsum added, the emission of ammonia (NH3) also decreases.

[0058] 2. Effects on pH and germination index

[0059] Compost samples were collected after turning the compost on days 0, 3, 7, 14, 21, 28, 35, and 42 from the beginning of composting and stored at 4°C for analysis of pH and germination index (GI).

[0060] Figure 3 The pH change trend of the samples during the composting process is shown in the figure. It can be seen from the figure that the pH of the FGDG5% and FGDG10% treatment groups with added desulfurized gypsum is lower than that of the CK treatment during the entire composting process. This is because the pH value of the desulfurized gypsum itself is low and the gypsum contains a large amount of SO4 2- It can react with NH3 to produce (NH4)2SO4 during the composting fermentation process, so the pH of the two treatments is lower than that of the CK treatment group. After composting, the pH values ​​of the CK treatment group, FGDG5% and FGDG10% treatment groups were 8.44, 7.40 and 7.48, respectively. Compared with the CK treatment, the pH of the pile decreased by 12.32% and 11.37% after adding desulfurized gypsum.

[0061] The samples taken at 0d after composting and 42d after composting were tested for germination index. The experimental results are shown in Table 2:

[0062] Table 2 Germination index (GI) of different treatment groups before and after composting

[0063] Experimental groups 0day 42day CK 79.17％±10.66％ 89.26％±5.43％ FDGD5% 77.87％±4.26％ 93.93％±5.04％ FGDG10% 70.59％±6.43％ 97.83±11.02％

[0064] From Table 2, we can see that the initial GI (germination index) of the three treatments is relatively high, which may be related to the properties of the cow dung raw material itself, but it does not meet the national standard (≥80%). And as the amount of desulfurized gypsum added increases, the initial GI value decreases, which is related to the fact that the addition of desulfurized gypsum changes the environment of the pile itself. From the data in Table 2, we can see that after 42 days of aerobic composting, the GI of the three treatments increased and reached the national standard, among which the FGDG10% treatment group with desulfurized gypsum added had a greater increase.

[0065] 3. Compost product nutrients

[0066] In the whole composting system, cow dung is the main nitrogen source, straw is the main carbon source, and desulfurized gypsum is the modifier. Before composting, the basic physical and chemical properties of the compost raw materials are tested. The test results are shown in Table 3:

[0067] Table 3 Basic physical and chemical properties of compost raw materials

[0068] index Cow dung Wheat husk straw Desulfurization gypsum Moisture content (%) 58.73±0.83 8.22±0.06 10.66±0.12 <![CDATA[pH a ]]> 9.27±0.021 8.04±0.057 7.79±0.021 <![CDATA[Conductivity a (mS / cm)]]> 7.66±0.38 4.99±0.078 7.07±0.27 <![CDATA[Organic carbon a (%)]]> 37.38±0.028 46.13±0.11 - <![CDATA[Total nitrogen a (%)]]> 2.65±0.053 0.69±0.005 - C / N 14.11±0.76 66.86±0.46 - <![CDATA[Total phosphorus a (g / kg)]]> 6.89±0.64 0.85±0.14 0.75±0.69 <![CDATA[Total potassium a (g / kg)]]> 18.99±0.18 10.90±0.52 0.44±0.045

[0069] Note: With superscript a The index is measured after air drying, and is only used here to indicate the processing method of compost raw material samples.

[0070] Compost samples were collected after turning the compost on days 0, 3, 7, 14, 21, 28, 35 and 42 after the start of composting. One part was air-dried, ground and sieved for testing indicators such as organic carbon, total nitrogen, total phosphorus, total potassium, total calcium and total sulfur content; the other part was kept fresh in a 4°C refrigerator for testing the content of available nitrogen.

[0071] Figure 4 The following is a trend chart of organic carbon (%), total nitrogen (%) and C / N of organic fertilizers in different treatment groups during composting (where a is organic matter, b is total nitrogen, and c is C / N). Since desulfurized gypsum is an inorganic solid waste, its organic carbon and total nitrogen content are almost zero. Therefore, when it is mixed into the compost, the organic carbon and total nitrogen (%) of the compost pile will increase. Figure 4 a, b) decreased compared with CK and their change trends were the same as CK, but their C / N changes were almost the same as those of the CK group ( Figure 4 c). Among them, the organic carbon degradation rates of the CK, FGDG5%, and FGDG10% treatment groups were 9.15%, 16.42%, and 9.76%, respectively. It can be seen that although the addition of desulfurized gypsum reduced the total organic carbon content, it increased the degradation rate of organic carbon and promoted the maturity of the compost.

[0072] Table 4 Physical and chemical properties of 42d organic fertilizer

[0073]

[0074]

[0075] As shown in Table 4, when desulfurized gypsum was added to the composting system as an improver, the total sulfur, total calcium and available nitrogen of the final compost product were significantly increased compared with the CK treatment, which increased by 79.54% to 187.61%, 144.45% to 210.53% and 39.91% to 633.7% compared with the CK treatment. The total sulfur and total calcium FGDG10% treatment group increased more significantly, increasing by 187.61% and 210.53% compared with the CK treatment; and the increase in available nitrogen in the FGDG5% treatment group was even greater.

[0076] 4. Conclusion

[0077] In summary, during the 42-day aerobic composting process, the addition of desulfurized gypsum to the composting system reduced the nitrogen loss in the form of ammonia by 74.77% to 85.17% compared with the CK treatment, and the carbon loss in the form of CH4 by 19.28% to 25.3%. After the composting, the pH values ​​of the CK treatment group, FGDG5% and FGDG10% treatment groups were 8.44, 7.40 and 7.48, respectively. Compared with the CK treatment, the pH of the pile body decreased by 12.32% and 11.37% after adding desulfurized gypsum. The organic carbon degradation rates of the CK, FGDG5% and FGDG10% treatment groups were 9.15%, 16.42% and 9.76%, respectively. The addition of desulfurized gypsum increased the degradation degree of the compost. The GI (germination index) was 89.26%, 93.93% and 97.83%, respectively, all reaching the national standard. The total sulfur, total calcium and available nitrogen of the final compost product increased significantly compared with the CK treatment, increasing by 79.54% to 187.61%, 144.45% to 210.53% and 39.91% to 633.7% respectively. The total sulfur and total calcium content of the FGDG10% treatment group increased more significantly, increasing by 187.61% and 210.53% compared with the CK treatment.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An organic fertilizer, characterized in that: The invention comprises the following raw materials in parts by weight: 4-6 parts of cow dung, 0.5-1.5 parts of straw and 5-13% of the total weight of the cow dung and the straw in the desulfurized gypsum.

2. An organic fertilizer, characterized in that: The invention comprises the following raw materials in parts by weight: 5 parts of cow dung, 1 part of straw and desulfurized gypsum containing 10% of the total weight of the cow dung and the straw.

3. The method for preparing the organic fertilizer according to claim 1 or 2, wherein The following steps are involved: S1. Raw material processing: crushing the straw to obtain straw powder, mixing the cow dung, straw powder and desulfurized gypsum to obtain a mixed material; S2. Composting fermentation: The moisture content of the mixed material is adjusted to 55-65%, and then filled into the composting device for sealed fermentation; S3. Aeration: Force aeration is performed on the mixed materials in the composting device every day, with an aeration rate of 0.7-1.0 L / min / kg of mixed materials. Aeration is performed once every two hours from 0 to 8 o'clock, and once every hour at other times. Each aeration time is 3-8 minutes. S4. Turning the pile: Turn the pile during the composting process and ferment the compost for 40 to 45 days to obtain organic fertilizer.

4. The preparation method according to claim 3, characterized in that: The straw is wheat straw.

5. The preparation method according to claim 4, characterized in that: The particle size of the straw powder segment is 2 to 5 cm.

6. The preparation method according to claim 3, characterized in that: The aeration rate is 0.88 L / min / kg of mixed material, and each aeration time is 5 min.

7. The preparation method according to claim 3, characterized in that: The time for turning the pile is 0th, 3rd, 7th, 14th, 21st, 28th, 35th and 42nd day from the start of composting, and the composting fermentation time is 42 days.

8. The preparation method according to claim 3, characterized in that: The composting device includes a barrel body 1 and a barrel cover 2. The barrel body 1 is provided with an aeration hole 4 at the lower side wall, and the aeration hole 4 is connected to the aeration device 3 through a second ventilation pipe 10; the barrel cover 2 is provided with a temperature measuring hole 5 and a three-way valve 6, one end of the three-way valve 6 is connected to a greenhouse gas collection device 7, and the other end is connected to an ammonia absorption device 9 through a first ventilation pipe 8.

9. The preparation method according to claim 8, characterized in that: The barrel body 1 and the barrel cover 2 are made of stainless steel.

10. The preparation method according to claim 8, characterized in that: The ammonia absorption device 9 is filled with boric acid solution and an indicator.

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