Goodrich SUGAR & CHEMICAL COMPLEX LIMITED
OFFERS
BAGASSE DRYING PLANT
FROM
CHINA AND GERMANY

Goodrich - 3 Pass Bagasse Drier
(Roller type drier)

  

Rader -Thompson Bagasse Drier
(Rotary drum type - for comparison)


Stern - Roger Bagasse Drier
(Rotary drum type - for comparison)

  

Fred - Hausmann Bagasse Drier
(Vertical suspension type - for comparison)

BAGASSE DRYING PLANT –

The process of manufacturing crystal sugar requires steam. By installing co-generation systems, the sugar industry now produces Electricity far in excess of their captive requirement & sells the surplus power to the grid.

Mill wet bagasse contains about 50% moisture. The calorific value of mill wet bagasse is 2280 kcal/kg. Use of driers to reduce the moisture content in bagasse before it is burnt, is regarded as a simple energy conservation measure. This bagasse drying system can also use the waste heat from the boiler flue gases for its partial heat requirement.

ADVANTAGES OF BAGASSE DRIER –

  1. Boiler efficiency goes up substantially & bagasse consumption comes down.
  2. Environmental problems associated with the combustion of wet bagasse are addressed to a large extent.
  3. Calorific value of dry bagasse increases more than proportionately.
  4. Clean - burning of dried bagasse increases the boiler life & reduces maintenance.
  5. Surplus dried bagasse can be sold to the nearby Paper mills, Briquetted Fuel makers & other fuel users.

CAPACITY OF BAGASSE DRIER –

Goodrich offers this most advanced technology from its associates in China & Germany. The bagasse drier is roller type drier, with two options–

  1. To dry wet bagasse from the initial 50% moisture to 40% moisture. –

    -capacity upto 100 tons per hour or 2,250 tons per day, based on input. This drier can use chimney temperature of as low as 1500 C.

  2. The same drier can also dry wet bagasse from 50% moisture to 25–30% moisture, provided the flue gas temperature in the chimney is up to 2000 C.

The cost of drying the bagasse is less than Rs. 50/- per ton, which includes the cost of electricity for drying, cost of labour, supervision & maintenance. However, the value addition by way of increased calorific value is around Rs. 200/- per ton, making the dryer system highly profitable.

TYPES OF BAGASSE DRIERS –

1. Stern Roger / Rader –Thomson (USA) drier -

This is a rotary drum type bagasse drier consisting of a long drum inclined to one end & slowly rotating on two pairs of roller assemblies supporting the drier at another end. The drum drier is rotated by means of a spur gear or chain drive through a speed reduction unit.

Wet bagasse is fed continuously at the elevated end of the drum. The hot boiler flue gases are sucked by an advanced draft fan through the rotary drum. As the particles of bagasse fall, they meet the hot gases either in parallel flow or in counter-current flow. During this, the bagasse gets partially dried. The extent of drying depends on the temperature of the flue gases, bagasse retention time in the dryer and other factors.

Fred – Hausmann (Switzerland) drier –

2.The Fred – Hausmann type bagasse drier is a vertical suspension type drier. Wet bagasse is distributed from the top of the drier & hot flue gases are admitted from the bottom of the drying column. Bagasse & hot flue gases travel in counter - current direction in the drying column. When bagasse is dried, a set of cyclone separators separate the flying particle of dried bagasse from the bottom of the drying column.

The bagasse drier offered by Goodrich has the following key components –

3. Goodrich – 3 Pass Bagasse drier –

In association with Italian & German designers and Chinese Equipment suppliers, Goodrich offers roller type tube drier for bagasse drying. This drier is widely used in large Particleboard installations all over the world, where the wood flake / bagasse is dried upto 3% moisture. More than 300 such installations are already in operation worldwide.

In the roller type drier, bagasse is fed through a rotary feeder into the rotating dryer drum. The particles are conveyed pneumatically in the first pass, whereas transport in the second & third passes is effected mechanically by the built-in lifting shovels. The dried particles and drying gases are separated in the high-efficiency cyclones, which are fitted with air-locks.

Schematic diagram of a 3 Pass Bagasse Drier -

This dryer can be operated using the recycled air from the boiler chimney. The advantages of Goodrich three-pass dryer are –

  1. Low investment cost & low drying cost.
  2. Low specific heat requirement.
  3. High temperature drop.
  4. Easy maintenance.

REASONS FOR DRYING BAGASSE –

A) Incremental calorific value

When any fuel is burnt, its heat generation capacity is indicated by a term ‘Calorific Value’, which means the quantity of heat generated by burning a unit weight of the fuel. The total heat generated by burning a unit of weight of fuel is known as Gross Calorific Value (GCV). If the latent heat of water vapour in the combustion of gases is not recovered, it is lost in the flue gases along with the sensible heat of the water formed by combustion. The balance quantity of heat is known as Net Calorific Value.

Water (moisture content of bagasse) has no calorific value, but on the other hand it absorbs heat in getting vaporized, and as such this process reduces the calorific value of mill wet bagasse.

All the constituents of mill wet bagasse with the exception of moisture are combustible. But the presence of water in bagasse reduces its fuel value, as a part of the heat value of bagasse is used for the evaporation of moisture content of bagasse, before bagasse can catch fire. Thus heat is wasted.

The lower calorific value of bagasse depends on the sugar % of bagasse & moisture content of wet bagasse. Prof. Von Britzehwitz developed a formula to calculate the calorific value of bagasse as under-

LCV
(Low calorific value of Bagasse)
= 7650 minus 18 times of sugar % bagasse,Minus 86.4 times of moisture % in bagasse.

For example, if the sugar content in bagasse is 2.5% & the moisture content is 50%, then –

LCV =7650 - (18 * 2.5) – (86.4 * 50)
= 7650 - (45 + 4320)
=3285 kcal/kg

If the same bagasse is dried up to 30% moisture, then –

LCV =7650 - (18 * 2.5) – (86.4 * 30)
= 7650 - (45 + 2592)
=5013 kcal/kg

After losing 20% water, the bagasse weight will be 0.80.
Hence 5013 * 80%
= 4010 kcal/kg

The incremental heat value after drying the bagasse is 725 kcal/kg (4010 – 3285) or 22% more, which stands in support of the drying cost of bagasse.

In another formula which is generally adopted, the calorific value of bagasse can be obtained by –

Btu / lb of Bagasse = 8550 F + 6935 S – 972 W
                                  100

where

F = Percentage of Fibre in Bagasse (assume 47.5% for mill wet bagasse & assume 66.5% for 30% moist bagasse)

S = Percentage of Sugar in bagasse (assume 2.5% for 50% moist bagasse & 3.5% for 30% moist bagasse)

W = Percentage of Water in bagasse (assume 50% in moist bagasse & 30% in partially dried bagasse)

In the above example, the calorific value is -

Btu/lb of bagasse =

   8550 x 47.5 + 6935 x 2.5 - 972 x 50
                                 100

       = 3748 Btu/lb

        or ¸1.8 = 2083 kcal/kg

After drying the bagasse up to 30% moisture, the values change proportionately and the increased calorific value is -

        = 8550 x 66.5 + 6935 x 3.5 - 972 x 30

        = 5637 Btu/lb

         or ¸1.8 = 3132 kcal/kg

After losing 20% water, the bagasse weight will be 0.80.

        Hence 3132 x 80%

        = 2505 kcal/kg.

Here also, increased heat value after drying the bagasse is 422 Kcal/kg (2505 - 2083) or 20% more.

Experiments have proved that by decreasing the moisture of bagasse from 50% to 40% & by varying the air intake of Boiler, the calorific value is increased by 30%. By using partially dried bagasse as fuel, the evaporation rate in the boiler will go up, thereby requiring less bagasse as fuel, resulting in saving of bagasse.

In another experiment, it has been indicated that Bagasse containing 20% moisture produced 27% to 39% more steam than mill-wet bagasse with 50% moisture (When both the figures are converted into moisture free basis).

Though the calorific value of bagasse increases as the moisture content reduces, drying of bagasse below 25–30% moisture is not recommended for boiler purpose, as there is a possibility of the furnace temperature going up, resulting in clinker formation with bagasse ash. At the same time, very dry bagasse is likely to fly away when confronted with forced draft & escape along the chimney without being burnt, which will also create pollution problems.

B) Heat recovery -–

Bagasse driers offer a great advantage of permitting the flue gas temperature to be brought down to the lowest level. Bagasse drying gainfully uses the flue gases.

C) Reduced air pollution -

Bagasse drying is considered as a method to solve air pollution problems in the Co-generation Plant.

D) Bagasse saving -

A 2500 TCD Sugar mill generates 750 tons of bagasse per day with 50% moisture. When the same is dried to 30% moisture, the increased califoric value even after taking into account the weight loss, is 20 – 22%. This implies that by drying bagasse upto 30% moisture, sugar factories can save 150 tons of bagasse per day with 50% moisture, which will be a saving of 24,000 tons on 160 days of working. The saved bagasse can be sold to the nearby paper factories after depithing & subsequent drying, or converted into Particleboard or MDF.

Energy balance on drying of bagasse –

Power consumption per ton of dried bagasse

20 KWH

Saving of bagasse per ton

200 kgs on 50% moisture initial basis

Generation of equivalent units of electricity from 200 kgs of saved bagasse

100 KWH

Net saving of Electricity

80 KWH

Monetary value of electricity generated from saved bagasse (assuming the value of power at Rs. 3/- per KWH for 160 days of working for a 7,500 TCD Sugar Plant, installing a 100 tons per hour bagasse dryer)

Rs. 10.80 crores

Net savings on bagasse drying

Rs. 8.64 crores

Notes: It is assumed that a Co-generation Plant attached to a Sugar Factory can generate 2.20 kgs of high-pressure steam per kg of bagasse & 4.40 kgs of steam are required to generate 1KWH of Power in the condensing mode.

Hence 2 kgs of saved bagasse can generate 1 KWH of power or 200 kgs of saved bagasse per ton can generate 400 KWH of power. A bagasse dryer plant of 100 tons per hour can save 20 tons of bagasse per hour or 450 tons per day or 72,000 tons per year on 160 days’ of working, which is equal to 3.6 crore units of electricity per year.

For more details, please contact –

Goodrich Sugar & Chemical Complex Limited

No. 16, 2nd Main, 2nd Cross,

AECS Layout 3rd Stage,

Sanjaynagar, Bangalore – 560 094,

Karnataka, India.
Ph: 0091 - 80 – 23411400

Fax: 0091 - 80 – 23410388

Email: rao@goodrichsugar.com

Website: www.goodrichsugar.com

  


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