Flaked rice is one of the most commonly consumed breakfast in the states of Maharashtra, Karnataka, Gujarat, Madhya Pradesh and Rajasthan. It is known by a number of names, including poha (Hindi), avalakki (Kannada), aval (Tamil) and atukulu (Telugu). It has played an important role in religious ceremonies for a very long time. Poha is easy to prepare and digest and many varieties can be made with it. But the poha manufacturing is one of the major polluting industries currently and is right now facing the serious challenge from the government to cut down on their emissions. In this article, we are highlighting the issues with current poha production systems and how poha millers can cut down on the pollution and save money at the same time.

Production Details:
Though there is no clear production data available, but it is estimated that about 10% of total rice production is used for flaked rice, expanded rice and popped rice. Orissa, Maharashtra, Madhya Pradesh, Chhattisgarh are the major poha manufacturing centers of India.

The process of poha production is explained below:

Different processes of manufacturing poha:soaking, conditioning, roasting, flaking, sieving

 

The Pollution Problem:
Out of these, roasting is one of the very critical process of the entire production which adds ‘crispiness’ to the poha and the color. Nowadays, continuous-type cylindrical roasters are commonly used for roasting the paddy. During the roasting process, the sand is heated to 170-220 deg Celsius. This heat is either supplied by burning natural gas or locally available biomass fuels (such as saw dust, rice bran/husk etc.) in the highly inefficient combustion chambers. When such biomass fuels are used, it contributes greatly to the environmental pollution because of the high ash/moisture content of the fuel and inefficient furnaces.

As observed in the industries of Bhatapara (Chhattisgarh) and Ujjain (Madhya Pradesh), some of the common features of these roasters are:

  • Convective heat loss due to lack of insulation: The furnaces of most of the roasters are designed with normal construction bricks and without any insulation.
  • Radiative heat losses due to manual ash removal: These furnaces also have an ash removal opening which also work as an inspection hole. The plant operator uses this to manually remove the hot ash from the furnace. This opening doesn’t have any door to close which results in high amount of heat loss through radiations.
  • High flue gas heat losses: The ash removal opening also let high amount of excess air to enter the furnace leading to high amount of heat being lost with flue gases. High excess air also leads to drop in the furnace temperature resulting in incomplete combustion of the fuel and often lead to black smoke coming from the chimneys.
  • Wrong selection of fuel: The industry relies majorly on cheap, locally available biomass fuels such as rice bran, saw dust, wood etc. Though the cost per kilogram of these fuels are very low, but these fuels often have high moisture and ash content resulting in heat losses. Due to this, more quantity of the fuel is required to supply a given amount of heat. This often leads to high monthly fuel cost bills and pollution.
  • Manual Operation: The ash removal opening also works as an inspection window. The plant operator inspects the color of the combustion chamber to judge the temperature of the chamber and then manually adjust the fuel feeding. The poor judgement can lead to excess or insufficient fuel supply, leading to change in the temperature of the furnace affecting the quality of the poha and the gaseous emissions as well.

What to do?
If you are a poha miller or you are planning to start one, make sure you pay close attention to the roaster heating systems. As evident, traditional furnaces aren’t the right systems as these have poor thermal efficiency and are highly polluting way of burning the fuel.

Pellet/multi-fuel burners have recently gained lot of attention as an effective way of producing heat for small systems in an automated and controlled manner. These pellet burners have an external combustion chamber where the fuel (usually pellets) is combusted and the flame is directed horizontally into the system using secondary air. Some millers in Ujjain have tried using pellet burners as an accessory to the traditional furnaces to roast poha. Though the system was able to solve the pollution issue using clean biomass fuels (such as pellets) but couldn’t improve the thermal efficiency of the system. Thus, horizontal firing systems aren’t a reliable method for this application. Additionally, higher costs of pellets have shown to increase the total fuel costs by 20-40% in such cases further reducing the attractiveness of such investments.

Hence, there remains an immediate need for a solution which effectively control the pollution but not at the expense of such a huge jump in the fuel costs. Steamax has been working closely with poha roasters and millers to develop a suitable technology and new biomass fuels for their application. If you are interested to know more about them, contact us.

 

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