GB/T 4921-1985 Determination of oxygen consumption and nitrogen oxides in industrial waste gases - Potassium dichromate oxidation and naphthylethylenediamine colorimetric method
Some standard content:
National Standard of the People's Republic of China
Determination of chemical oxygen demand and nitrogen oxide in industrial waste gas Potasslum dichromate oxidation and uaphthylethylenediamine colorimetric method
UDC 628.64.828
31:543.482
GB 4921—85
This standard is applicable to the determination of oxygen demand and nitrogen oxide in fulminate of mercury waste gas after treatment or initial treatment. Applicable scope Oxygen demand value 2~200mg/L, oxidation 1-100mg/m.
The oxygen demand value in this standard refers to the content of certain organic gases and reducing gases in waste gas that can be reduced by potassium dichromate under specific conditions, measured in terms of oxygen consumption value.
In this standard, oxidized ammonium refers to the sum of nitrogen oxides such as nitric oxide and nitric oxide, calculated as nitrogen dioxide. 1 Principle
1.1 Fulminate waste gas contains a variety of organic substances such as alcohols, esters and aldehydes, and reducing substances such as nitric oxide. To evaluate the effect of waste gas treatment, the waste gas is passed through potassium dichromate-sulfuric acid solution and heated to reflux. The treatment effect of these substances is measured by the consumption of potassium dichromate. 1.2 Potassium dichromate is titrated with ammonium ferrous sulfate, with o-phenanthroline as the indicator. K,Cr,O--6FeSo4+7H,SO= K,SO,+Cr2 (So,),+:Fe2 (SO)a+7H,0 (colorless)
1.3 Nitric oxide in the waste gas is oxidized by potassium dichromate to become nitrogen oxide, which can be absorbed by sodium hydroxide containing a small amount of sodium arsenite, and then colorized with aminobenzenesulfonamide and diamine. Colorimetric analysis is performed. Industrial nitric acid diazotizes p-aminobenzenesulfonamide, and then connects with distilled ethylenediamine to produce red azo dye. NHH,PO.
+ HNO2
National Environmental Protection Agency 1985-01-18 Issued N - n- h,Po.
SO,NH2
NHCH, CH, Nh,
So, nh, Nhch,Ch, nh.
1985-08-01 Implementation
2 Instruments
In addition to general chemical analysis instruments, the following should be available: GB 4921-86
2.1 Sampling device with five absorption tubes: See the figure below. #Oxygen consumption value Nitrogen oxide sampling device schematic diagram
1, 2, 3-Large absorption flask, for containing oxidation, 4, 5-Large absorption tube, for containing absorption liquid, 6-Irradiation bottle: 7-Flowmeter: 8-Spring clip for regulating air flow: 9-Vacuum pump 2.2 Conical flask with reflux condenser (500ml). 2.3 Spectrophotometer.
9 Reagents
The reagents used in this standard are analytically pure unless otherwise specified, and all percentage concentrations are weight volume percentages (w) unless otherwise specified
3.1 Oxidizing solution: Weigh 49g potassium dichromate, add 600ml water to dissolve, add 300ml sulfuric acid while stirring, cool and dilute with water to 1000ml. 3.2 Absorption solution: weigh 4 g of sodium hydroxide and 1 g of sodium nitrate and dissolve them in water, dilute to 1000 ml, 3.a Potassium dichromate standard solution (0.25 N), accurately weigh 12.2579 g of potassium dichromate (standard reagent, dried at 105 ° C for 2 hours) and dissolve it in water. At 20 ° C: dilute to 1000 ml in a volumetric flask 9.4 Ammonium ferrous sulfate standard solution (0.25 N): weigh 98.0 g of ammonium ferrous sulfate, add 40 ml of 1:1 sulfuric acid, add water to dissolve, cool and dilute to 1000 ml with water, if there is turbidity, filter it clearly. At the same time, calibrate with 0.25 N potassium dichromate standard solution (calibration results are valid on the same day).
9.5 Ferrocyanide indicator: Weigh 1.485g of o-phenanthroline (C12HIgNzH,0) and 0.695g of ferrous sulfate, dissolve in water, dilute to 100ml, and store in a brown bottle.
3.6 Silver sulfate.
3.7 Concentrated sulfuric acid: 1:1
3.8 Para-nitrobenzenesulfonamide solution (2%): Weigh 2g of para-aminobenzenesulfonamide (also known as sulfonamide, H,NC.H,SO,NH,) and dissolve in 95ml of water, add 5ml of 85% phosphoric acid, mix, store in a brown bottle, and store in the refrigerator. 8.9 Sodium nitrite standard stock solution (NO, (.1mg/ml): Accurately weigh 0.1500g of sodium nitrite that has been pre-dried at 105℃ for 2h, dissolve it in water, and dilute it to 1000ml with a volumetric flask. Store it in a brown bottle. This solution contains 0.1m nitrite ion per milliliter. 9.10 Sodium nitrate standard solution (nitrate content 1μg/ml): When using, dilute the above (3.9) sodium nitrite standard stock solution 100 times with absorption liquid to make it contain 1μg nitrite ion per milliliter. . 4 Operation steps
4.1 Drawing of standard working curve
To determine nitrogen oxides, a standard working curve must be drawn in advance, and the method is as follows. 4.1.1. Accurately add 0, 2, 4, 6, 810 ml of sodium nitrate standard solution to six 25 ml colorimetric tubes with stoppers, then add 10, 8, 6, 4, 2.0 ml of absorption liquid, mix, add 10 ml of 2% p-aminobenzenesulfonamide and 1.4 ml of 0.1% naphthylethylenediamine solution, mix, and place in a dark place for 15 minutes. GB 4921—86
4.1.2 Use a 2cm colorimetric tube and adjust to zero with a blank solution at a wavelength of 540nm to determine the absorbance. 4.1.3 Use the micrograms of nitrite content as the horizontal axis and the measured absorbance as the vertical axis to draw a standard working curve. 4.2 Sample collection and storage
4.2.1 Mercury waste gas should be sampled at the outlet of the treatment pipe and before entering the smoke exhaust pipe or smoke exhaust duct. Since the concentration of harmful substances generated during the operation cycle is uneven, it is stipulated that the average sample of each operation cycle should be collected for analysis. Under normal production conditions, The average sample from the start of adding fulminate of mercury compound to the end of discharging of all fulminate of mercury compound is used as the sample for analysis. 4.2.2 When sampling, the temperature and air pressure of the sampling point should be recorded so as to convert the sampling volume into the sampling volume under standard conditions. 4.2.3 Fill each of the human-shaped absorption tubes (see 1, 2, 3 in Figure 2.1) with 20 ml of oxidizing liquid, and each of the two large absorption tubes (see 4, 5 in Figure 2.1) with 20 ml of absorption liquid, and then connect them in series as shown in the figure. Samples can be collected by vacuum pump or exhaust method. For fulminate waste gas that has only undergone preliminary treatment, it is better to use drainage method for sampling. 4.2,4 For deep treatment For fulminate of mercury waste gas, extract a sample of one operation cycle (about 50-60L) at a rate of 100ml per minute, and then pump air at the same rate for 3min (the air pumped in is not counted in the sample volume). 4.2.4.1 For fulminate of mercury waste gas that has only undergone preliminary treatment, extract a sample of one operation cycle (about 5-6L) at a rate of 100ml per minute, and then pump air at the same rate for 10min (the air pumped in is not counted in the sample volume). 4.2.5 After sampling, transfer the oxidizing solution in the absorption tube to a 100ml volumetric flask, dilute with water to 1/3, mix well, and prepare for measuring the oxygen consumption value. Transfer the absorption liquid in the absorption tube to another 100ml bottle, dilute with water to the mark, mix well, and prepare for the measurement of nitrogen oxides. 4.2.6 The sample is allowed to be stored for one week under airtight and light-proof conditions. 4.3 Determination of oxygen consumption value
4.3.1 Take 10ml of the sample from the 100ml volumetric bottle and put it into a 500ml conical flask with a reflux condenser, add 23ml of water, slowly add 27ml of concentrated sulfuric acid, add 0.5g of silver sulfate, shake to dissolve, add several glass beads or several glass beads with a diameter of about 1 Ⅱ, and make the L end of the glass beads exposed to the liquid surface, place them crosswise, and heat and flow together. During the reflux process, use a small amount of water to wash down the water droplets on the inner wall of the condenser every 20min, and let it flow for 2h, then rinse the inner wall of the condenser with a small amount of water, cool it, and remove the reflux condenser. 4.8.2 In a conical flask, add water to 140 ml, add 2 drops of o-phenanthroline indicator, and titrate with 0.25N ammonium ferrous sulfate standard solution until the solution changes from blue-green to reddish brown to the endpoint. 4.3.3 When analyzing the sample below, take another 3×20ml of the oxide and put it into another 100ml volumetric flask, dilute it to the mark with water, mix well, and take the sample in the same way as in 4.3.1-4.3.2). 4.4 Determination of nitrogen oxides
4.4.1 Pipette 1ml of sample into a 25ml colorimetric tube, add absorption solution to 10ml, and mix well. 4.4.2 Add 10ml of p-aminobenzenesulfonamide and 1.4ml, mix well, add stopper, and place in dark place for 15min. 4.4.3 Take another 10ml absorption solution and operate in the same way as above (4.4.2) as reagent blank for colorimetric zeroing. 4.4.4 Use 2cm colorimetric blood, wavelength 540m, adjust to zero with reagent blank, and measure the absorbance of sample solution (4.4.2). 1.4.5 Find the corresponding nitrite content from the standard working curve by absorbance. 5 Calculation
5.1 Convert the sampling volume into gas volume under standard conditions according to formula (1). 273×P
273+t*760
Where: %——sampling volume under standard conditions, L; - on-site recorded sampling volume, L;
! Temperature at sampling point, C: wwW.bzxz.Net
P—atmospheric pressure at sampling point, mm1g. (1)
5.2 Calculate the oxygen consumption value according to formula (2).
GB 4921-B5
(VW) ×N×8
Oxygen consumption value=
Wherein, V--the sampling volume under standard conditions, LV--the volume of the standard solution of ammonium ferric sulfate consumed when titrating the blank oxidizing solution, ml; - the volume of the standard solution of ammonium ferric sulfate consumed when titrating the sample, ml: ~The volume of the solution taken from the 100ml volumetric flask, mlN is the current concentration of ammonium ferrous sulfate (calibrated with potassium dichromate standard solution on the same day). 5.3 Calculate the nitrogen oxide content according to formula (3). Nitrogen oxide (NO×, mg/m3)=
0.85 × ×
Wherein: W
The nitrate content found on the curve drawn by the standard.1,! ——Convert to the multiplier sample volume under standard conditions, L, V.
-The volume of the sample taken from the 100ml volumetric flask for determination, ml0.85-The coefficient of conversion of nitric oxide (gas) or nitrite. 6 Matters needing attention
6.1 It is allowed to use a vacuum pump to extract multiple samples, but each sample must maintain the appropriate flow rate. (2)
6.2 When determining nitrogen oxides, if brown precipitate appears and the color is abnormal, it may be caused by the excessive concentration of nitrogen oxides in the sample. A small amount of sample should be taken and repeated. When the concentration of nitrogen oxides is low, more samples can be taken. 6.3 Immediately after sampling, record the sampling volume in liters and remove the sampling head from the pollution source detection point. Place the sampling tube in a clean atmosphere to allow clean air to continuously enter and drive the nitrogen oxides in the upper space of the oxidation liquid into the suction tube. 6. If the air is not clean, make the air pass through a series of 250ml Münster washing bottles (the first one is filled with 100ml of oxidizing liquid and the second one is filled with 100ml of collecting liquid) to purify the air. If the air is particularly dirty, the air should be washed by connecting No. 3, 4 to No. 5, 6 Meng washing bottles in series according to the situation.
7 Allowable error
7.1 When the oxygen consumption value in the exhaust gas is below 2m/., the allowable error is 0.3; when the oxygen consumption value in the exhaust gas is above 2m/L, the allowable relative error is 16%.
7.2 When the nitrogen oxide concentration in the exhaust gas is lower than 5 mg/m^, the allowable error is 0.6mg/m; when the nitrogen oxide concentration in the exhaust gas is higher than 5mg/m3, the allowable relative error is 15%.
Additional remarks:
This standard was proposed by the former State Council Environmental Protection Leading Group. This standard was drafted by the State-owned Yangtze River Power Plant and the State-owned Longjiang Power Plant. The main drafters of this standard were Yang Dejun and Guan Enbao. The Ministry of Ordnance Industry's environmental protection department was entrusted with the interpretation of this standard.
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