Integrated Biomass-Fired Palay Drying System

Arnold R. Elepaño

18 March 2006IRG-P, Ortigas

INTRODUCTION

The Global Environmental Facility (GEF): Promoting the Adoption of Renewable Energy by Removing Barriers and Reducing Implementation Costs

Capacity Building to Remove Barriers to Renewable Energy in the Philippines (CBRED) Project

1. Policy, Planning and Institutional Capacity Building

2. Market Services Institutionalization

3. Information and Promotion Services

4. RE Initiatives Delivery and Financing Mechanisms

5. Training Program

6. RE Technology Support

RE Engineering Service Industry Development

• Develop a capacity building program for local RE engineering firms, which includes technical support for process improvement

• Develop a registration program for engineering firms and service companies aimed at providing greater end-user assurance on the quality of engineering services provided by these firms

• Develop a monitoring and evaluation system to evaluate effectiveness and efficiency of the registration program

• Provide inputs to the RE Advocacy and Promotion Subcontractor in developing a promotional program

Objectives

• Introduce the fundamental concepts and assumptions of an integrated biomass-fired palay drying systems design

• Demonstrate the use of a simple computerized calculation program to determine sizes and number of units of equipment for palay drying system with rice hull furnace

Integrated Palay Post-Production Processing Flow

• Immediate transport of the harvested and threshed palay from the farms to the processing plant.

• Classification, weighing and issuing of farmer’s delivery receipt.

• Drying. Incoming grains will be dried. Rice hulls will be used as fuels.

• Palay Storage. Storage bins will be used for better insect and inventory control. The type and number of varieties will be considered in the design.

• Milling and Grading. The milling process includes palay cleaners, de-stoner, rubber roll husker, palay separator, whiteners / polishers, plant sifter, length grader, blender and automatic bag weigher. A final stage is the blending of head rice and broken rice according to market specifications.

• Weighing and Bagging. Rice will be bagged into 50 kg/ bag before delivery. The by-products such as brewers rice and rice bran will be bagged into 75 kg/bag before shipping to users.

Existing Rice Post Production Technologies in the Philippines

Operation Technology Capacity Usage, % Losses, %

Harvesting Manual 99.8 2.0 –3.0

Reaper

Combine

2.4 – 3.8 ha/d

4.5 – 8 ha/d

nil 0.2 –0.4

Threshing Manual 0.05 – 0.1 t/h/person 31.0 2.1 – 4.2

Axial-flow 0.5 – 1.0 t/h 69.0 0.1 - 1.6

Drying Sundrying 24 kg/m2 86.0 1.0 – 5.0

Flatbed

Recirculating

Continuous

1.0 - 5 t/batch

1.2 – 10 t/batch

2.0 – 10 t/h

14.0 0.4 – 1.2

Milling Kiskisan 0.1 – 0.3 t/h 10.5 55 – 63*

Cono

Rubber roll

0.5 – 2.0 t/h

0.5 – 2.5 t/h

33.2

56.1

65*

65 – 70*

Storage Bag 3.4 m3/t 99.0 2.0 – 6.0

Bulk 1.7 m3/t 1.0 nil

Palay Drying

• The basic technology to preserve the fresh harvest is to dry it to 14% for storage

• Actual physical loss in the practice of highway-sun drying to range from 2.14 to 8.7%, averaging about 5%

• Delay in drying while waiting for the sun, causes general darkening of the grain, and yellow discoloration of some kernels

• The key technology therefore for minimizing losses and improving grain quality is the appropriateness and availability of grain dryers to arrest biological deterioration

Target Users of Drying Technology

Sys Target User Candidate Technology

Auxiliary Facilities

1 Individual farmers Low cost 0.t ton batch dryer

Moisture meter

2 Small farmer groups, Seed growers, Custom dryer contractors

Flatbed batch dryer (2-6 ton/batch), rice hull furnace

Shed, cleaner, weighing scale, moisture meter

3 Large farmer cooperatives, Local government service dryers, Millers 1 tph

Batch recirculating dryer (4-6 ton/batch), rice hull furnace

Service building, storage bins, cleaner, weighing scale, receiving bin, moisture meter

4 Federation of farmer cooperatives, LGU service dryers, Millers 3-6 tph

Batch recirculatign with tempering bins (10 ton), rice hull furnace

Building, cleaner & grader, bins, moisture meter, materials handling equip

Drying Plant Design Considerations• Site selection (accessibility, power,

water, peace and order, cost of land)

• Rice production (yield, area, irrigation)

• Economics (market demand, competitiveness, capital availability, credit)

• Cooperative (management, technical capability, labor availability)

Mechanical Dryers

Drying Principle: heat and mass transfer

• The process of thermal drying consists of removing the moisture in vapor form, absorbing the vapor into the drying air and removing it from the palay being processed.

• The drying air transfer sufficient heat to the moist palay to evaporate the moisture and absorb the resultant vapor, that is, heat and mass transfer process occurs between the moist palay and the drying air.

Psychrometry

• Psychrometry deals with determining thermodynamic properties of moist air and using these properties to analyze conditions and processes involving moist air.

• Humidity ratio, relative humidity, specific volume, enthalpy, dry-bulb and wet bulb temperatures are provided in a psychrometric chart.

Rice Hull

• Rice hull properties vary widely in space and time, like many biological materials.

• The bulk density of rice hull is about 100 kg/m3 or 1/6th the density of coal or 1/9th that of fuel oil

• The heating value of rice hull is 3,400 kcal/kg (14MJ/kg) or about the same as wood waste, or 1/3 of fuel oil

• Rice hull contains 14-16% fixed carbon, 54-70% volatile matter, 17-26% ash. The ash consists of 90-95% silica.

• Depending on the variety, rice hull range in length from 5 to 10 mm and the width is 1/3 to ½ of the length.

PADISCORCyclonicRice HullFurnace

PADISCOR cyclonic furnace

• Cyclonic motion is generated inside the combustion chamber while the fuel is burning. Ash is separated from the air resulting in a clean flue gas.

• Pneumatic feeder carries rice hull from feed hopper to the combustion chamber.

• Rotary grate discharges the ash continuously at a rate synchronized with the fuel feed rate.

• Secondary air is also injected tangentially in the combustion chamber, increasing burning efficiency and separation of ash and air.

Combustion Model

The combustion model uses the equation of the thermodynamic heat and mass balance. It is based on the following assumptions:• The system is at steady state.• The combustion is complete with negligible amount of

carbon monoxide generated.• Solid particle products (unburned carbon and ash)

emerge at the same temperatures as the gas product.• Ash consists of silica, SiO2, the thermal properties of

which are known.

Pneumatic Feeder

• It must provide uniform feeding of rice hull for uniform combustion.

• Angle of incline surface = 75° to ensure downward flow of rice hull

• Capacity of hopper should be enough for 3 hour operation

Combustion Chamber

• Grate area must be 50 to 60 kg/h.m2 or 840 MJ/h.m2• Combustion chamber volume must be 40 to 60 kg/h.m3

or 840 MJ/h.m3

(source: Gerzhio AP & VF Sahochetov. 1960. Grain Drying and Grain Dryers)

Primary Air/Secondary Air

• Primary air and secondary air must be provided at certain ratio to provide complete combustion of rice hull. Assumed ratio of primary to secondary air = 25/75 to 35/65.

• Excess air of over 60 percent is recommended.

Rice Hull Ash Removal

• Ash must be discharged at regular rate to prevent clogging of the combustion chamber. Ash disposal must be synchronized with fuel feeding.

• In general, cyclone furnace needs a high air flow, so that ash residue can be conveyed through the cylindrical section