Wednesday 13 June 2007

Reusing waste plastics as fuel

Plastics are so adaptable in use that their impacts on the ecosystem are far-reaching. Irresponsible dumping of plastic bags block drains, obstructs the permeability of the soil and causes problems for groundwater recharge. Plastic upsets the soil microbe activity, and once eaten, can kill animals. The estimated quantity of municipal sold waste generated in India every day is 131,000 tonnes or 48 million tonnes annually (2003). Plastics constitute at least seven per cent of this waste or 9,200 tonnes daily. Unlike other wastes, plastics do not degrade easily and is usually advised not to burn them as it emanates poisonous gases during its burning in open air at temperatures less than 400 degree Celsius. It is generally estimated that our households contribute major share of plastic wastes in urban areas in the form of used carry bags, bottles, packets of milk, etc. Packaging constitutes 52% of plastics consumption. The tendency of people in urban areas is to throw these plastics along the roads, as they cannot process them or recycle them in their compounds and it becomes a ‘burning’ problem for Municipalities & Corporations.

Recycling plastics
Most people think that all of their waste plastics can be recycled, but that's not true. Plastics in category 1 (Polyethylene Terephthalate) and category 2 (High Density Polyethylene) are mainly recycled. It is usually called down-cycling because the waste plastics are converted into low-grade plastics. The cost of conversion is also high making the down cycling less attractive and also the conversion process cannot be repeated forever. Plastic categories 4 through 7 -- such as lids, sheets of plastic and wrappers -- traditionally are discarded at recycling centres. But they are of value because they generate heat when burned. Plastics, being derived from petroleum, have the energy content similar to petroleum fuels. The main concern about burning plastics is when type 3 plastics (mainly PVC) are incinerated, because of the chlorinated compounds they contain. There have been attempts in India to use waste plastics in developing road surfaces with it. This does not dispose of the toxins but simply spreads it around, much like in the case of landfills.

Plastics as fuel
James W. Garthe of the Pennsylvania State University has developed a process in 1995 to convert all types of dirty plastics into fuel nuggets. The intent of the nugget process was to direct used plastics into a new raw material stream for energy recovery, either co-fired with coal in community and agricultural boilers or burned directly. The process was developed for waste agricultural plastics, yet it works with plastics found in all sectors of society. Both film and rigid thermoplastics can be accommodated.

The 'plastofuel', as Garthe calls it, overcomes most major impediments in plastic waste management. The Garthe machine is a hydraulic compactor with a heated die. Roughly shred and cleaned waste is fed into the hopper, from where a ram pushes it into the heated die. At exit of the die, the extrudate is sliced by a hot-knife into nuggets. The nuggets may then be stored forever and transported economically. These nuggets can be used as a high-energy fuel supplement for coal-fired applications. In such applications, it is found that plastics will not adversely affect emissions levels as the plastics are burned at very high temperatures. At more than 1,200 degree Celsius, plastics burn completely without leaving out toxic solids and without black, toxic smoke usually associated with burning plastics at the backyards.

A blessing in disguise
In the Garthe machine, the die is heated just enough to fuse the outer skin of the nugget. The energy required for this is minimal. It is in fact a compaction process, readying the waste for storage and transportation. The calorific value in the plastic waste remains trapped. Thus, the energy gained from nuggets is more than what was put in to create them. Cottage level entrepreneurs (similar to Kudumbashree units in Kerala) can generate income by using such a machine, after collecting the waste plastics directly from the source (like the households).

Commercial utilisation of waste plastics
1. GR Technology Company, Ltd. of Seoul, Korea
A new technology, developed by GR Technology Company, Ltd. of Seoul, Korea, burns plastic pellets made from waste plastics of all sorts, initially from agricultural sources. William Bang of GRT arranged to ship one of these burner units to Penn State for testing. It was installed to heat a high tunnel and a greenhouse at the Penn State Horticulture Research Farm. Eventually the burner/boiler system was modified to burn plastofuel nuggets, which were significantly larger than the pea-sized pellets. Testing of the 120,000 kcal/hr heater unit in Korea showed the system meets US EPA emissions standards.

2. Whitehall Cement Plant of Lafarge North America
Lafarge North America, which has begun fuelling the kilns at its Whitehall Township cement plant in part by burning the scraps of non-recyclable plastic. Lafarge says burning plastic could keep more than 10,000 tons of the substance out of landfills each year, while also cutting the amount of coal used by the Whitehall cement plant. The plant, which has burned used tires for several years, now can derive up to 45 percent of its power from tires and plastic. Plastic also costs less than coal, which means the new power source will cut Lafarge's fuel bills. The state Department of Environmental Protection approved the plastic plan after a five-year review, ruling it would not exceed standards for chemical release.

3. Unique Plastic Waste Management & Research Co Pvt Ltd, Nagpur, India
Prof. Mrs. Alka Umesh Zadgaonkar, Head of Department of Applied Chemistry at the Nagpur based G. H. Raisoni College of Engineering invented an Environment friendly catalytic process for disposal of waste plastic. The invented process involves degradation waste plastic using `catalytic-additive’ and is different from the generally existing pyrolytic processes. The laboratory scale set-up was developed in batch mode in which individual as well as mixed plastics were successfully converted in to fuels. The products obtained in the process are Liquid hydrocarbons, Gas and residual Coke. Prof Alka & Dr. Umesh Zadgaonkar started a company named Unique Plastic Waste Management & Research Co Pvt Ltd, which is converting plastic wastes into fuels equivalent to petrol and LPG on a commercial basis.

Summary
This commercial utilisation of waste plastics give great scope for people engaged in waste collection to earn more income, saves more fossil fuel, keeps our neighbourhoods clean and saves landfill space. Policy makers should take into consideration the failure of attempts to ban plastics of various thicknesses.

Read also:
PSU team turning waste plastic to fuel
Waste plastic technology
Burning plastic for fuel a win-win situation
Alka Zadgaonkar wrings plastic waste for profit
Plastic to Petrol: Conversion of waste plastic to energy

2 comments:

Vincent2012 said...

With the rapid advance of the global economy, the demands of rubber market to carbon black become more and more.

Plastic Pyrolysis Process Machinery

Al said...

The technology to produce pellets of waste plastic for burning is most interesting and exciting.
However, I note this report was made in 2007.
What has happened since then? Is it progressing? Has it been shelved for some reason?
Many countries around the world continue to pollute the environment by casting out waste plastic onto the roads and into the oceans. This surely is an urgent matter.

There was an error in this gadget