Safety Research And Design for Rotary Drum Dryer
Rotary drum dryer needs hot air stove to be its heat source.During the drying process,there’s possibility to cause fire.Because some sparks from the stove may go into the drum.So it is very important to kill the sparks before it enters into the drum.SIMEC has made the research and design to solve this problem.Here below we take an example and try to explain how we do.
Size of dryer: ￠2.9m*15m triple layer rotary drum dryer
Wet material: 45% moisture content lignocelluloses, in the shape of fluffy granules,bulk density 512kg per cubic meter;
Dry material:moisture content is required to be 15%, bulk density 256 kg per cubic meter.
Fuel for the stove: lignocellulose granule, diameter>3mm,moisture content 15%.
Lignocellulose
Sparks
Its combustion led by airflow will cause lots of sparks which maybe dangerous for the lignocelluloses drying process.
So for the design of combustion stove,we should consider more on the following two issues:
1. Combustion efficiency of the fuel;
2. Sparks prevention solutions;
Since the moisture content of fuel will be dryed lignocelluloses,about 15%.It’s easy to be ignited.And the combustion is stable when there’s enough oxygen supply.The heat will be induced by strong airflow and go into the rotary drum dryer.
On the stove,a blower will be installed to blow oxygen into combustion chamber.The stove is fixed bed type.The ash settling room is under the combustion chamber.The design makes the stove suitable to be customized on site.The sparks active prevention system adopts traditional reliable technology which does not rely on any electronic product.
There’re two types of designs for sparks prevention:
1. Sparks settling channel;
2. Sparks separating cyclone.
Please see the details in the following parts of this report.
Specifications of Stove and Sparks Settling Channel
Structure and Fire Bricks
Structure and Fire Bricks
1.Hot air stove:
Ligno-cellulose has about 18.000 J/g calorific value in working state with water content of 14,5 %.To produce 7 TPH dry lingo-cellulose(15% moisture content), the stove’s burning surface area will be 6 M2.The size of stove can be made to be 3000mm long(5 pcs of fire grates in the length direction),2040mm wide(12 pcs of fire grates in the width direction).Type of the blower will be 3.2A-2.2Kw.
The overall size of stove is 3600mm long,2780mm wide,2000mm high.Between the steel shell and fire bricks wall,there’s 100mm thickness insulating layer for heat.
Considering the length of the stove,the fuel adding inlets will be on the sides.There’re two inlets on both sides that bring convenience to fuel adding and combustion inspection.
2.Sparks Settling Channel
The overall size of sparks settling channel is 5140mm long,1500mm wide,2000mm high. Between the steel shell and fire bricks wall,there’s also 100mm thickness insulating layer for heat.To achieve effective elimination of sparks,we make the design to include 5 units of sparks removing barriers.On every spark barrier,there’s one blow hole for air.The width of the barrier is 260mm.The gap between every two barriers is 500mm.The air holes are staggered up and down.So the airflow will move in the form of “S” wave.
Under every spark barrier,there’s a door to clean up the dropped spark ash.When the sparks impact the fire bricks,they’ll be killed and fall down,then become to be ash.
On every air hole,a filter screen will be installed.It’s made of 316 stainless steel that can work in 1400 ℃ high temperature.There’re two layers for each filter screen device.
Filter Screen
The filter screen will stand on skidway which makes it easy to be disassembled.The skidway device is also made of 316 stainless steel.The filter screen device is fixed by screw on the wall of spark settling channel.
Manufacture analysis for stove and sparks settling channel:
| No. | Name | Unit | Qtty | Specs. |
| 1 | Furnace door | pcs | 4 | Material:casting iron;fuel inlets. |
| 2 | Fire grate | pcs | 60 | Material:casting iron |
| 3 | Furnace beam | pcs | 6 | Material:casting iron |
| 4 | Furnace corner | pcs | 5 | Material:steel plate |
| 5 | Fire grate drawbar | pcs | 5 | Material:steel plate |
| 6 | Blower | set | 1 | 3.2—2.2kw |
| 7 | Spark filter screen | pcs | 5 | Material:316 stainless steel,thermostability |
| 8 | Standard brick | Pcs | 6860 | 240X120X5mm |
| 9 | Knife brick | pcs | 2658 | 240X120X5X3mm |
| 10 | Furnace door low brick | Pcs | 2 | 400X300X5mm |
| 11 | Furnace door dome brick | Pcs | 2 | 400X300X5mm |
| 12 | Furnace shell | pcs | 1 | 3600 X2780X2000mm |
| 13 | Shell of sparks settling channel | pcs | 1 | 4140X1500X2000mm |
| 14 | Skidway of filter screen | unit | 5 | Material:316 stainless steel,thermostability |
| 15 | Fire clay | bag | 95 | For furnace construction |
| 17 | Furnace cement | bag | 25 | To make the roof of furnace and sparks settling channel |
| 17 | Refractory slag | bag | 75 | To make the roof of furnace and sparks settling channel |
| 18 | Ring mould | Unit | 2 | Mould for furnace roof |
| 19 | Mould of air hole | Unit | 5 | To make air hole in sparks settling channel |
| 20 | pearlstone | bag | 150 | To make heat insulating layer between furnace shell and fire-proof wall |
Specifications of Sparks Separating Cyclone
Cyclone Separator of Sparks
This is the second solution for sparks elimination which is called sparks separating cyclone.The air speed at its inlet is about 15 m/s ~ 20 m/s.The hot air goes into the cyclone as tangential wave.The high speed swirling airflow will move inside the cyclone.Since the sparks are more heavy than hot air,the sparks will be thrown out via cone end into sparks dust collecting box. Meanwhile,the hot air will go into the rotary dryer through the outlet of cyclone.The sparks will not go into the dryer.
The cyclone is made of 316 stainless steel which can work in 1400 ℃ high temperature.Around the cyclone,it’s poured by fireproofing material.
Comparing with sparks settling channel,the weight of cyclone separating device is much less.But the former is more suitable to be customized on site.
Here is also indirectly heating stove.The fire will not touch the hot air directly.Its furnace is not so huge.The fuel feeding system is quite smart for granula fuel.The combustion efficiency will be good.
More important thing is heat exchange efficiency.The stove is also designed to recycle the waste heat which’s emissioned from the furnace chimney,especially when it provides heat for a rotary dryer.Please see the sample drawing as follow:
Here is also indirectly heating stove.The fire will not touch the hot air directly.Its furnace is not so huge.The fuel feeding system is quite smart for granula fuel.The combustion efficiency will be good.
More important thing is heat exchange efficiency.The stove is also designed to recycle the waste heat which’s emissioned from the furnace chimney,especially when it provides heat for a rotary dryer.Please see the sample drawing as follow:
Indirect Heating Furnace
Combustion Chamber