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Address: No.12 Huanghe Road, Changshu, Jiangsu, China.
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120 Tons per day Formalin 37% Plant
Description of Process Flow
This quotation selects a Off-gas Circulation Process with Reboiler, the introduction of which is given as below:
A.Formaldehyde reaction flow
Methanol is pumped out by methanol pump from methanol measuring tank and it is sent to evaporator when the methanol liquid level is controlled through measuring.
After the air is filtered by air filter, it is sent into air preheater by roots blower. The preheated air is sent to mixer for mixing.
0.15MPa steam comes into steam filter from steam pipeline. After it is filtered, it comes into mixer. The ratio between steam flow and methanol flow is 0.5~0.7 (mol ratio)
The above mentioned methanol gas, air and steam is mixed in mixer, then it comes into reactor. The temperature of mixing gas is controlled around 110℃ to prevent producing condensate, reducing filtering effect, changing gas composition. After the mixing gas comes into reactor, oxidation exothermic reaction drastically happened with silver catalyst. In order to maintain safety, high efficiency reaction condition, 3 feedstocks are needed to be maintained in certain ratio to maintain best reaction temperature, which is between 620℃ and 640℃
Reactor protection
Reaction temperature reaches 620～640℃ in normal reaction condition. In order to avoid destroying reactor, demineralized water is needed to be used for cooling. Demineralized water used by reactor for cooling is heated and vaporized and steam is produced for the use of other heaters. At the same time, mixing gas temperature reduced to 150℃ from 620～640℃. Make use of waste heat completely to reduce energy consumption. Demineralized water for cooling is produced from condensate and collected in condensation water tank. And it comes into reactor steam drum through boiler water, then it comes into cooling part of reactor.
When reactor is in emergency condition, protect the whole plant through interlock device.
1) High temperature alarm in first stage: when reaction temperature is above 650℃, the high temperature alarm device alarms to warn the operator adjust the ratio among air, methanol, steam to recover the condition until it is normal.
2) Limiting alarm in second stage: when temperature reaches 700℃, the roots blower stops running automatically.
B. Formaldehyde adsorption flow
The gas generated in reactor(the temperature is around 150℃) comes into bottom of formaldehyde 1#absorption tower, and it is circulating adopted through spraying by cooled crude formaldehyde. The flow is as following:
1) First step adsorption——1# tower circulating absorption, formaldehyde concentration at bottom of 1#absorption tower is 37%. Formaldehyde at bottom of 1# absorption tower is sent into 1# heat exchanger through 1# circulation pump and after it is cooled & heat exchanged, it returns to the top of 1# absorption tower. The temperature of liquid at the bottom is controlled 60～70℃.
2) Second stage absorption——absorption of down part of 2# tower: formaldehyde at bottom of 2# absorption tower is sent to 2# heat exchanger through 2# circulation pump and after it is cooled& heat exchanged, it returns to the middle part of 2# tower. The temperature of circulation liquid at this stage is controlled 40~50℃.
3) Third stage absorption——absorption of up part of 2# absorption tower: formaldehyde at the middle part of 2# absorption tower is sent to 3# heat exchanger through 3# circulation pump after it is cooled & heat exchanged, it returns to up part of 2# tower. The temperature of circulation liquid at this stage is controlled at 30℃
At last, the off-gas is discharged from the top of 2# absorption tower. The demineralized water is sent into by pump. The temperature of discharged off-gas is not higher than 35℃ (at summer). The off-gas from top of absorption tower is sent into incineration device, after the off-gas reaches the standard through incineration, than is can be discharged into air.
Specification of Product and Feedstock
1) Specification of Feedstock
The methanol feedstock shall at least conform to the requirements in Chinese Standard Industrial Methanol for Acceptable products, which is given as below:
| Item | Index | ||
| Superior Product | First Class Product | Acceptable Product | |
| Purify ≥ | 99.9% | 99.9% | 99.85% |
| Chroma ( Pt-Co)≤ | 5 | 10 | |
| Density(20℃),g/cm3 | 0.791～0.792 | 0.791～0.793 | |
| Temperature range(0℃,101325Pa),℃ | 64.0～65.5 | ||
| Boiling range (including 64.6±0.1℃) ℃≤ | 0.8 | 1.0 | 1.5 |
| Potassium permanganate time test min ≥ | 50 | 30 | 20 |
| Water miscibility test | Pass the test(1+3) | Pass the test(1+9) | - |
| Water content ％ ≤ | 0.01 | 0.15 | - |
| Acidity as HCOOH ％ ≤ | 0.0015 | 0.0030 | 0.0050 |
| Alkalinity as NH3 ％ ≤ | 0.0002 | 0.0008 | 0.00015 |
| Carbonyl compound as CH2O ％ ≤ | 0.002 | 0.005 | 0.010 |
| Evaporate residue ％ ≤ | 0.001 | 0.003 | 0.005 |
| Sulfuric acid wash test/Hazen (Pt-Co) | 50 | 50 | |
2) Specification of Product
| S/N | Component | Index |
| 1 | Formaldehyde | 37% |
| 2 | Methanol | ≤1 wt. % |
| 3 | Formic Acid | ≤0.01 g/100 ml |
| 4 | Chloride | ≤0.0025 g/100 ml |
| 5 | Ashes | ≤0.01 g/100 ml |
