Waste to Energy
Incineration is the most widely used process. Municipal waste is incinerated and the heat is captured in steam generators and used to power steam turbines to produce electricity. It has been deployed around the world for many years. However, early deployment was associated with “belching smokestacks.” This image has caused widespread public opposition to incineration. Technically, it is reliable and cost effective. However, getting incinerators permitted is all but impossible in many areas.
During the last 10 to 15 years, efforts have been expended to find non-incineration methods for diverting waste from landfills and capturing value. Waste segregation has developed for MSW. It is used to capture a substantial portion of the waste for recycling – certain plastics, paper, cardboard, and metals. However, the residuals are still sent to a landfill. The economics are dependent on large scale operations and close proximity to recycling centers. This technology is not suitable in many small to intermediate size communities as the transportation costs to recycling centers can exceed the value of the product.
Anaerobic digestion is limited to select feedstocks and has not been widely adopted. Pyrolysis and gasification have evolved to fill the need for more robust processes that can handle a wide variety of wastes. However, of note, these processes can work in concert with waste segregation and nearly eliminate the need for landfill capacity. The processes can also process a wide variety of wastes with little or no process modification required. They are versatile in that they can also produce a variety of products to meet local needs. Lastly, the developers claim they can address smaller markets with capacities of a few hundred tons per day. Public acceptance is mixed. While more favorable than for incineration, there is still concern over toxic emissions. In reality, a properly designed gasification system can produce very low emissions – especially when the syngas is used for chemical synthesis.
The biggest disadvantage for both pyrolysis and gasification is market maturity and cost effectiveness. The processes are well understood. However, long term, reliable, economic operation at large scale (200 tons/day and above) has not been widely demonstrated.