Circulation Fumigation Technology and Precautions in Steel Silo You Should Know

With continuous development and large-scale promotion of circulation fumigation technology, large storage and insecticidal problem in deep layer of steel silo has been gradually solved.

Compared with conventional fumigation technique, circulation fumigation technique can not only lower its cost and pollution and chemical residue for environment and grain, achieving synergistic fumigation in many ways and improving the insecticidal effect, but also can maintain air concentration for a long time. 

However, because of configuration of fumigation equipment, air tightness of silo, operation and other objective reasons, insecticidal effects in different silos are different in the fumigation process. So they are difficult to achieve ideal effects. Only through related preparatory work and factor control in the process of fumigation, we can ensure grain safety and improve insecticidal effects of circulation fumigation.

Circulation Fumigation Definition

The so-called circulation fumigation is to install a pipe inside or outside the silo to form the closed loop of fumigation circulation including circular fan, ventilation pipe/silo, circulation pipe and grain pile. The phosphine generator will pass the gas into circulation pipe. Under the conditions of air tightness, circulation fumigation system would force the fumigation air to circulate in grain pile by the pressure produced by circular fan in order to achieve the fumigation effects. This method has the characteristics of high automation, fumigation time control, long service life and low maintenance cost, which is almost not affected by the outside environment. So it is generally accepted by most of enterprises.

Circulation Fumigation Procedure

Air tightness of silo is good or bad, this would determine the success or failure of circulation fumigation. The detection of silo tightness can adopt "Half-life of pressure " method, that is, under the case of empty silo, first make suspected air-leaking point sealed, pressurize to the silo through the fan, then get the evaluation with the U pressure gage. The valuation should not be preset over high so as not to damage air tightness, generally controlled within 500-800Pa. When the pressure gauge reaches a predetermined valuation, the fan can be stopped, close the valve, record the time. When the initial pressure valuation becomes in half, the time is seen as half-life of pressure.. The longer half-life of pressure is, the better air tightness is; conversely, air tightness is worse.

The air tightness of the silo mainly depends on silo body, silo roof, bottom gate valve, the contact parts of silo wall and its roof, the sealing process of the contact parts of output steel cone and bottom plate.

Before fumigation, the sealing process is the key to determine the effects of fumigation, therefore, before sealing treatment the soap water detection can be used to find the air leaking point through pressure test, which is conducive to aimed sealing treatment.

Circulation Fumigation Control

Phosphine Concentration Test

Before circulation fumigation, a complete, effective and feasible set of the scheme should include the preparatory work, sealing treatment measures, the arrangement of test points of fumigation concentration, detection frequency, etc.

The factors of influencing effects of fumigation process include phosphine concentration, circulation frequency, sealed time, etc. Among them, phosphine concentration is the core factor that influences insecticidal effects. Therefore, to improve insecticidal effects as much as possible, phosphine concentration and sealed time should be differently determined according to the different needs of grain temperature and insect species in circulation fumigation process.

Below is the reference table of phosphine concentration of circulation fumigation in different sealed times and temperatures as different insect species.

Insect	Temperature (℃)	Sealed time
		14 d	21 d	28 d
Susceptible insect: Corn weevil, Long legged beetle, Tribolium confusum, etc.	>25	200	150	100
	20-25	250	200	150
	15-20	-	250	200
Resistant insect: Rhyzopertha dominica, rice weevil, Tribolium castaneum, etc.	>25	300	250	200
	20-25	350	300	250
	15-20	-	350	300

Therefore, we should always have a good master of the concentration of phosphine fumigation in silo in the process, in order to make proper adjustment timely for the value we want. So we should be good at the followings:

Check Phosphine Concentration Inside or Outside Silo at Any Time

We check phosphine concentration inside or outside silo at any time and master the change of time and regular pattern to silo and phosphine concentration, which would help us to carry out the works of remedy, circulation and air tightness test of silo. For different silos, different grains or the same silos in different periods, they are different in phosphine concentrations. To grasp concentration inside the silo, the main purpose is to kill the insects; to grasp the concentration outside the silo, the main purpose is to ensure the safety of the operators and inspect sealing effects. In order to facilitate the direct check of phosphine concentration in silo, we should increase its check holes, and install check device below the circular fan in each silo.

Control of The Amount of Carbon Dioxide

To control ratio of carbon dioxide and phosphine well is also necessary and important, which can make phosphine fully be taken away and lower the temperature, reducing the possibility of explosion during the fumigation. This can also enhance the toxicity effect of phosphine on adult insect and improve insecticidal effects.

Circulation Frequency

The circulation frequency is to enable mixed air of phosphine to reach rapid and even distribution in the in silo using circulation technology by mechanical means in order to achieve the effect of killing insects thoroughly.

Circulation frequency directly affects the fumigation effects, but it does not mean that the more the number of circulation fumigation is, the more evenly phosphine air is mixed, the more thoroughly the insects are killed. Indeed, there is a direct relationship between the factors of different storage times and grain amounts, temperature difference between inside and outside of silo, sealing effects, etc.

In order to improve circulation effect, reduce the resistance, we should use carbon dioxide to expel the air in the pipe utterly to form good channel, and then start phosphine circulation fumigation.

Flyer Company is expertise at circulation fumigation. We have accumulated rich experience in technology and construction. If you need to carry on similar project, please feel free to call us, we will sincerely provide best service with you!