Proceedmqs of the 7th Internatumal Workmg Conference an Stored-product Protection - Volwrne 1

Study on different duct systems for ventilation and fumigationin silos

Sun RUl, Zheng Guozhu, Zhao Zenghua , Yue mmg , Lu jianhua , Zhu Qmgzhong, Long jmhang , FuXmgqiang and Zhang Chengguang!

Abstract

Aiming at the characteristics of silo storage, Tianjm GramBureau designed a multifunctional duct system forventilation and methyl bromide and phosphme fumigation aswell as controlled atmosphere storage A senes of tnalsproved that the system was effective and practical for use mvertical silos

Introduction

The construction of vertical Silos has been developed mChma since the 1990s At present, it covers more than 50%of the total storage volume m Tianjm area Dunng thiscourse of development, some of the traditional methods oftechnological management for grams m honzontal storagehave become unsurtable for the changed type of storageTherefore, the need of new methods and facilities such astemperature mampulation and msect control has ansen Theauthor has pursued the development of multifunctional ductsystem since the 1990s for ventilation, recirculationfumigation, modified atmosphere storage and the reuse ofsurplus fumigants This paper presents the design and asenes of tnals

Design and Trials

Mechanism of the duct system for ventilation(MDSV) III small silo

· Research orgamzation Tanggu Gram Storage of TianjmGram Bureau· Penod of study 1987 -1989· Storage selected Brick-constructed small silo With 7 Omm diameter and 10m m height which has capacity of 150t· The components (Fig 1) air inlet, air-supplying Pipe,ventilating pipe and air outlet

I Tianjm Gram Bureau. 34 Iiefang Road. Hepmg Distnct , Tianjm300041 , Chma

The air mlet was fitted at the outer bottom of the Siloandwas connected With a movable fan The air-supplying ductwas placed m annular along the bottom of the silo SiXventilating pipes were placed radiantly on the bottom ofthe Silo at equal distance An air outlet was set into theupper part of the silo wall

Fig. 1. Duct system ill silos for mechamcalventilation

Table 1 shows that the use of the designed system forcooling gram was satisfying The air-flow m gram pile waswell distributed Without dead spaces It could be used fortreating heated gram m a comparatively short penod andregulating gram temperature close to air temperature

Fumigation duct system (FDS) III small-Sized silos

· Research organization Puji Road Gram Storage ofTianjm· Time of study 1982· Storage selected A small bnck-constructed SIlo of 200tgram capacity WIth 6 Om m diameter and 13m m heightwas used for the trial· The components AIr inlet, annular pipe at the bottom ofthe Silo, and SiXfumigant distributors (Fig 2)SiXfumigant distributors With perforations were installedat the base and close to the mner wall of the Silo Theupper outlets of distributors were sealed and the mlets ofthem were connected With the annular pipe A gas inletpipe was connected With the annular pipe and the otherSide of it was led to the outside of the silo for gaseousfumigant entrance

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Proceedmqs of the 7th Internaiumal Worktng Conference on Stored-product Protectwn - Volume 1

Table 1. Result of ventilation with open air for gram cooling m a small silo according to the designed duct system'

AIr temp C'C) Gram temp C'C)

Max Mm Av Max

Before ventilation After ventilation

Mm Max Mm AvAv

1 20 16 18 3 2 2 5-4 -2• Ventilation was conducted from 20 p m to 8 a m daily and the accumulated time was 36 hrs

Table 2. Changes of phosphme concentration m stored wheat pile of the silo'

Depth below the surface Hours after phosphme application (g/rrr')of stored wheat (m) 5 29 51 102 150

Center position o 5 1 5 o 009 o 05 o 20 010

2 5 2 0 1 0 o 05 o 50 010

4 5 2 0 1 0 o 05 010 010

6 5 2 0 1 0 o 05 010 010

Side position o 5 20 o 2 o 05 010 010

2 5 2 0 o 1 o 70 o 50 o 00

4 5 2 0 o 2 o 50 010 010

6 5 2 0 o 5 o 20 o 20 010

• Variety red wheat, Weight 175t, Dose rate calculated With zinc phosphide, wheat pile Sg/rn", space 3g/m3

FIg. 2. Funugation duct system III medium and small silos

• Result of phosphme fumigationThe applied phosphine was generated by the reaction of

zmc phosphide WIth diluted sulfuric acid The dose rate of

• Penod of study 1984 -1986· Storage selected Silos In Jun LIang Cheng Rice Mill ofTianjin WIth 7 Om in diameter and 3 5m In height,constructed WIth reinforced concrete and has a capacity of1000t

· The components connecting mouth of the fan, mside silo-annular-gas-supplymg Pipe, radial gas-flaw-pipe and gas-return pipe (Fig 3)

· Dose rate and resultsThe total applied dosage of methyl bromide was calculated

on the baSIS of 50g/m3 for the stack and 25 g/rrr' for spaceThe changes of methyl bromide concentration at differentpositions and the obtained ct products are shown In table 3The mortality of Infested Insects was 100% after 120 hours

ZInC phosphide was Sg/m3 for 168-hour exposure Acomplete kill of Infested insects was obtained m storedwheatThe changes of phosphme concentration at different layers

and positions are shown In table 2

Methyl bromide recirculation duct system (CFDS)in large-sized silos

Large silos m China are approximately 30m In height Witha capacity of 1000t As IS known to all, the Installation ofrational ducts for fumigant gas recrrculation IS needed Thedesign and trial was done as follows. Research organization Jun Liang Cheng Rice Mill

exposure

Flg.3. Methyl bromide recirculation duct system (CFDS) III

large-Sized silos

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Proceedwgs of tlU' 7th lnienuuionai Workmg Conference on Stored-product Protectwn - Volume 1

Table 3. Changes of methyl bromide concentration m a large silo and the obtamed ct products

Depth (rn) below the Hours after apphcation (g/m3) Accumulated ctsurface of wheat 7 25 52 70 85 product (g'hr/m3)

Center of stack 1 9 5 4 5 8 8 4 6 3 7 521 7

14 7 0 6 8 130 4 4 5 3 645 4

27 174 6 35 2 18 2 7 8 6 8 3563 7

Side of stack 1 3 7 4 8 7 8 4 5 4 8 440 1

13 1 0 4 6 7 3 3 7 4 5 375 1

29 1 9 7 3 6 8 4 0 5 4 447 5

Multifunctional duct systems in silos

The expenmental multifunctional duct system for Siloswas fit for coolmg gram by mechamcal ventilation,fumigation WIth vanous fumigants such as methyl bromideand phosphme, controlled atmosphere storage and the reuseof surplus gaseous fumigants (Fig 4)

II

t

II

I

Fig 4. Multifunctional duct system III silos

The components of the system consist mainly of air mlet,

annular pipe at the outside bottom of the silo, radial pipes atthe mside bottom, vertical pipes surroundmg the mner wallof the Silo, T-shaped pipe at the mner top, bottomconnectmg pipe With outside Siloand air outletThe condition of mechanical ientilaiion. unih. themultifunctiona! dud systemWhen the system was used for mechamcal ventilation. the

air flow entered the outer annular pipe through the mlet andthen mto the radial pipe at the bottom Later on, It flowedmto the gram stack While the system was used for negativepressure ventilation, the air flowed m the oppositedirection• Research organization Tanggu Gram Storage of Tianjm• Penod of study 1990 - 1991· Storage selected Capacity of 240t With 6 6m m diameterand 15m m height• Result of ventilationThe method of mtermittent mechamcal ventilation was

adopted on January 9 - 13 for 12 hours a day The totalventilation time was 48 hours At the end of ventilation. thegram temperature was lowered by an average of 10 13'Cand the temperature difference among layers and positionswas less than 1'C (Table 4)

Table 4. Effectiveness of total 48-hour mtemuttent ventilation With the multifunctional duct system for coolmg stored wheat1U a vertical Silo

Gram temperature ('C)

Before ventilation (20 00, Jan 9) After ventilation (08 00. Jan 13)

Depthrm) East West South North Center East West South North center

8 15 9 15 3 17 0 15 2 17 7 o 0 o 9 o 8 o 9 o 46 18 2 11 1 9 0 9 5 109 o 9 1 1 1 3 o 9 1 2

4 8 7 7 3 8 1 7 8 8 9 o 2 1 3 1 2 1 6 1 8

2 100 8 8 8 9 8 8 8 1 o 2 o 2 o 3 o 1 1 1

1 112 9 8 10 1 8 8 9 5 1 5 o 9 1 2 1 0 1 4

The use of multifunctional duct system for methylbromide recirculaium [umuxitnonResearch organization Tanggu Gram Storage in Tianjm

· Penod of study 1990 -1991· Storage selected 6 6m m diameter and 15m m height,With a capacity of 240t

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Proceedmqs of the 7th Iniernaiumal Workmg Conference on Stored-product Protection - Volume 1

Table 5. Concentration (g/rrr") changes of methyl bromide at different positions m wheat pile dunng recirculation fumigationWith the mulufunctional duct system (Dose rate 40 g/rrr' for gram pile, 15 g/m3 for air space)'

Depth Hours Accumulated ct(rn) 1 3 7 12 24 48 product (g' hrvrrr')

Atr 1 37 8 33 31 24 27 3 19 9 1176 9Center 1 37 8 33 27 3 21 9 19 9 16 2 1052 1

5 32 6 30 25 2 19 9 15 5 16 2 927 957 31 32 24 18 8 16 2 15 899 49 31 27 3 23 5 20 17 15 905 65105 29 27 3 24 17 2 15 5 12 5 775 1

Side 1 33 31 27 3 22 5 22 5 16 2 1072 53 33 32 6 29 18 8 19 9 15 1005 55 32 6 29 25 2 23 17 12 5 917 17 29 27 3 21 23 15 5 13 874 99 30 27 3 23 17 16 2 14 849 5

Average 32 48 30 82 25 79 20 41 18 63 15 45 962 92• Gram red wheat, weight 240t

Dunng recirculation fumigation, methyl bromide enteredthe gram pile through the bottom connecting pipe, innervertical pipe and the T-shaped Pipe at the top inside of theSilo Then It flowed through the inner bottom radial pipes,the circular pipe at the outer bottom and the connecting pipeat the outer bottom to form a circulation routeWithin 1 hour after methyl bromide apphcation , a

comparatively homogeneous diffusion of the gas wasobtained The average ct product of different posrtionsreached 962 92 (Table 5) after 48 hours recirculation andall of the insects were dismfestedThe use of multifumctumal dud system for phosphinerecirculaium. funuqaium.The author paid pnor attention to the danger of explosion

of phosphme under mappropnate flow rate and high

concentrations The speed of phosphme generation byalummum phosphide tablets and the gas flow rate werestnctly controlled dunng the trial· Research orgaruzation Tanggu Gram Storage m Tianjm· Penod of study 1991-1992· Storage selected 6 6m m diameter and 15m m height,has a capacity of 240t (red wheat)The dose rate of ALP tablet (effective component 56%)

was 6g/m3 and the total of It was applied onto the surface ofstored wheat The reciculation system started after 24 - 28hours of tablet application until the end of 120 hoursexposure No alive insects were found at different positionsof the gram pile soon after the tnal The changes ofphosphine concentration at different positions are shown mTable 6

Table 6. Concentration changes of phosphine at different posrtions m wheat pile dunng recirculation fumigation m the use ofmultifunctional duct system (mg/L) •

Hours after ALP application Accumulated ct product

12 24 36 48 72 96 120 (rn-hr-L)

Atr space Depth of gram pile 1 0 2 0 2 5 2 6 2 5 2 2 2 0 249 6Centert m)

1 o 8 2 0 3 0 2 5 2 2 2 0 1 8 237 03 o 8 2 0 3 0 2 6 2 0 2 0 1 9 235 25 o 8 2 0 2 1 2 4 2 0 2 0 1 8 219 67 o 9 2 0 2 0 2 1 2 0 1 9 1 7 210 69 o 9 2 5 2 0 2 1 2 0 1 7 1 7 212 0105 1 0 2 5 1 8 2 3 1 8 2 0 1 8 217 8

Side 1 1 1 2 0 3 0 2 5 2 5 2 0 1 8 247 83 o 9 2 0 2 0 2 2 2 0 1 9 1 6 211 25 o 9 2 0 2 0 1 8 2 0 2 0 1 8 208 87 o 9 2 0 1 8 2 0 2 0 1 8 1 8 205 29 o 9 2 0 1 8 2 0 2 0 1 8 1 7 204 0

Average o 91 2 08 2 25 2 26 2 08 1 94 1 78 221 0• doserate ALP 6g/m3

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Proceedmqs of the 7th Iniernatumal Workmg Conference Oil Stcred-produc! Proiectum - Volume 1

Utilizatum. of the multifunctional duct system fOi reuseof surplus fumuxint gas m oihet jumioationIn common fumigation practice, there IS usually some

surplus undecomposed fumigant gas m the container at theend of treatment which can be used for other silo that needsfumigation This was done m a tnal for both silos equippedwith multifunctional duct systems The specific way was toconnect the two systems through two blowers for senesrecirculation under sealed condition The fumigantconcentration m the recervmg silo was measured after aboutone hour operation Additional fumigants were applied to thereceiving silo according to the fixed dosage of fumigation

· Research organization Tanggu Gram Storage of Tianjm· Penod of study 1990 - 1991Storage selected Red wheat stored m a vertical Silo

· Method The supplying silo was fumigated with methylbromide at dosage rate of 40g/m3 for gram stack and 15g/rn' for space exposed 48 hours While the fumigation ofthe supplying Silo was frrnshed, the surplus methylbromide was circulated into the receivmg Silo with the aidof senes operation of both multifunctional duct systemsThen a supplemental dosage of methyl bromide wasbromide transference, which IS shown m Table 7

Average MeBr concentration m supplying Silo (g/m')

Table 7 Result of reusing surplus methyl bromide with the aid of senes operation of multifunctional duct systems

Before supplying After supplying

Average MeBr concentration m receiving silo

after two hours transference (g/m3)

15 83 6 92 6 08

Discussion

A senes of field tnals have proved that the design of themultifunctional duct system IS successful m the mam Smce1991, quite a few research achievements have been spreadand applied m Tianjm area, which has achieved fairly goodsocial and economic benefits The mstallation of duct systemfor vertical silos has supenonty of effective use offumigantsThere are some points for attention should be stressed as

follows. Gastightness of storage IS the key factor for successful useof the systems The cntenon of Tianjm gram system ISthat the half-hfe penod of air pressure should be no lessthan 1 nun especially m the use of carbon dlOxlde fordlsmfestlon

. When the system IS used for methyl bromide fumlgatlOn,generally the ventilation capaClty should be 1 5m 'lhr t ,but It should be less than thiS capaClty when used forphosphme reClrculatlon fumigation

Dunng the release of cylmdenzed methyl bromide mto thesystem under low air temperature conditions, a heatingdevice should be allocated to prevent the block-up of theoutlet pipe

References

Lu Jianhua , Zhao Zenghua , Lru Omg , Hu Shutian and QIJmshen 1994 Study of circumfluent fumigation Withphosphine for killing stored- gram msects m Silos InHighley E , Wnght E J , Banks H J , and Champ B Red , Proceedings of the Sixth International WorkingConference on Stored-product Protection, Canberra,Australia. Apnl1994 I, 116 - 119Sun RUl, Guan Lianghua, Zhang Chengguang , Liu Chunheand Lu Jlanhua 1992 Ductmg systems for slio fumlgatlOnm gram storage In Navarro Sand Donahaye E ed,Proceedmgs of International Conference on ControlledAtmosphere and Fumigation m Gram Storage Wmlllpeg,Canada, June 1992 3-D - 351

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