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 |
