Solid Waste Management and Insufficient Electricity Supply Issues

In most emerging economies current methods of managing municipal solid waste (MSW) generated by households and commercial enterprises, construction debris, wastewater treatment and medical waste is often by way of land-filling in both designed landfills and, very often, in ad hoc, informal landfills.  Frequently, the landfills are improperly designed, are illegal or are not operated as properly designed sanitary landfills with little or no management and controls. 

In many cases, waste in the urban setting is not managed at all, particularly in areas of informal settlements.  Waste from such informal communities easily and quickly ends up in waterways, drains, canals and streams and rivers, thus polluting the waterways and exacerbating severe flood events, which annually cause death and destruction, and substantially increasing the incidence of disease, costing the national and local economies very dearly in terms of money, damaged lives, lost employment opportunities and work hours, property, a degraded environment and other lost socio-economic opportunities.  As developing countries become emerging economies, so quickly does the increase of growth in the migration of people from rural to urban areas, thereby rapidly increasing the problem of urban waste management.  Pressure to provide land for settlement in and near these urban centers means there is increasing difficulty in identifying suitable landfill sites, thereby making landfills an inappropriate solution to urban waste management. Moreover, landfills generate methane, which in itself is a potent greenhouse gas leading to global warming.

At the same time, a growing economy and the increasing migration to urban areas results in a rapidly increasing demand for electrical power.  Management of this increased demand in emerging economies is often difficult and limited because of insufficient non-renewable energy resources, increasing costs of physical plant and fossil fuels, which are impacted by global, external factors often beyond the control of the city or community suffering the electrical shortages.  With electricity demands of developing economies being met increasingly through imported diesel and natural gas fuel, the cost of electricity has steadily risen with the rising global costs of fossil fuels.  The use of fossil fuels also generates a less visible cost in the form of increased emissions and the generation of greenhouse gases that lead to global warming, increased ground-level ozone and a degraded urban environment that brings its own set of costs from dealing with related health issues and concomitant reduced productivity of the urban population and a degraded urban environment.

The AET/HPEG group provides its clients with the use of the "EnvirOcycler" GTO, an existing technology that has been successfully used for over 30 years globally in the forestry industry. The earlier generations of the EnvirOcycler were first developed in the 1970s in Canada. Approximately 40 biomass EnvirOcycler were built over the following years for sawmill companies using wood residue as feedstock. Many of these EnvirOcyclers are still in operation providing output heat used to dry lumber, plywood presses and veneer dryers.The design of the EnvirOcycler has been improved to be able to use wet MSW as its feedstock and effectively address solid waste management issues.

The EnvirOcycler is designed and engineered to provide reliable heat with no harmful emissions, meeting US EPA Emissions Regulations; only benign by-products are produced from the gasification and thermo-oxidizing process at less than 5% of the volume of the source MSW depending on ash content. These by-products are generally used as additives to pavement and concrete mixtures. The heat can be used to generate electricity or, alternatively, it can be used as industrial process heat.

AET's EnvirOcycler GTO facility in Malaysia

Overview of the Technology

AET’s patented EnvirOcycler technology addresses the two growing urban problems of growing municipal solid waste and decreasing supply of electricity in a single package by converting MSW to energy through a process that is viable and clean with low emissions using a two-stage gasification/thermal oxidizing unit that generates up to 105 GJ/hour per unit from any wet biomass such as MSW. 

This technology’s need for a minimum of 35% moisture content in the solid waste means that energy from the process does not need to be parasitized for drying the waste prior to processing, as is required in the other gasification technologies on the market, which means more energy is available for generating electricity, thereby resulting in a higher output efficiency.

Assuming an average of 1.5 kg of MSW generated per capita, a single EnvirOcycler unit can convert the organic fraction of municipal solid waste into heat for communities ranging in population size from 184,000 to 305,000, depending on the waste’s moisture content and size of its organic fraction.

Typical EnvirOcycler GTO mass-energy balance (click on image for larger view)

An EnvirOcycler project generates about 80 construction jobs and as many as 100 permanent jobs for its operation and management.  Given the incoming waste is mixed, the non-organic fraction of the waste can be separated and sold by the community as recyclable materials.

The EnvirOcycler produces no furans, dioxins or NO_x as emissions.  The fly and bottom ash can be sold as a soil conditioner, as a liming agent, or as a Portland cement additive to make stronger and more durable concrete. 

A single EnvirOcycler unit produces 105 GJ/hr from municipal solid waste.  More units can be added on site for higher power generation and a higher rate of MSW disposal.  The heat can be converted to electricity or sold directly to energy consuming facilities such as hospitals or to industrial facilities for air conditioning, ice manufacturing or process heating purposes such as agricultural product processing facilities.  HPEG proposes to establish such small scale industries near its EnvirOcycler plants using the heat from the plants, thereby creating more ancillary temporary construction and permanent jobs.

A 105 GJ/hr EnvirOcycler unit produces 6.5 MW of gross power.  Approximately 1.0 MW of parasitic power demand is required to operate the MSWTE plant, leaving 5.5 MW of net power that can be sold to an electrical utility as grid electricity.

Competing gasifiers use updraft, downdraft, plasma, fluidized bed, incineration or aerobic digestion technologies. Regardless of the specific technology details, several fundamental differences in approach distinguish the EnvirOcycler from competitors' products:

• Other systems strive to create a synthetic gas to fuel some sort of separate engine. This requires supplementary clean-up and gas handling equipment that may use external energy and cause complications in the engines. EnvirOcycler gasifiers are pure heat machines that supplies heat for direct use or to drive an electric turbine cycle.

• Other systems must use carefully controlled feedstock with small particle sizes and low moisture content to sustain their reactions. This requires elaborate feedstock screening, pre-treatment, and sometimes drying equipment that may use external energy. The EnvirOcycler gasifier accepts waste streams with particles sizes from 1/4-inch to 4-inches and with a moisture content of 35% to 55%, provided it has been screened to remove metals, plastics, and non-combustible materials, many of which are recoverable and can be sold for added revenue. It uses the waste stream itself to fuel the gasification process.

• Other systems consume fuel very quickly (in the order of seconds at most) to sustain their reactions. This leaves almost no time to adjust to differences in demand or fuel composition. The EnvirOcycler has a fuel residence time of about an hour, a lower first stage burner temperature of 650ºC (to avoid vaporizing sodium and chlorides that precipitate on the walls of the gasifier and the ash grate) and can accommodate 15-second step changes in demand, allowing plenty of time to adjust for differences in fuel composition. The consequence of the slower reaction rate of the EnvirOcycler is that it tends to be much larger than other machines of equivalent energy output.

Adopting the EnvirOcycler technology as an important component of a municipal waste management program provides a number of immediate and significant benefits to the target communities:

• Converts non-reusable waste as a renewable energy resource into combustible gases for electricity generation and other economic benefits while providing an environmentally-friendly solution to municipal solid waste management. EnvirOcyler feedstock can be MSW, sewage treatment sludge, construction wastes, medical wastes or agricultural wastes;
• Increases local energy security by producing electricity for local supply using a renewable energy resource while generating revenue by selling electricity to the local electrical grid;
• Utilizes MSW and other high moisture content wastes to offset the use of expensive imported fossil fuels for generating electricity and heating. A single 105 GJ EnvirOcycler unit will offset the equivalent of more than USD 10 million in imported fossil fuels each month, assuming the price of oil is at USD 100 per barrel;
• Reduces the direct production of greenhouse gases from electricity generation by offsetting the use of fossil fuels;
• Eliminates the need for new landfill sites or the expansion of existing landfills to accommodate municipal solid waste streams from urban areas, therefore allowing that land to be put to more productive and economic use;
• Reduces the risk of soil and groundwater and surface water contamination and of the spreading of disease from landfills, particularly if the need for landfill is eliminated;
• Reduces the risk of rat-borne leptrospirosis (where this is a serious problem) as the waste in urban areas is more effectively managed and removed from the urban environment;
• Reduces environmental pollution to rivers, land and air in jurisdictions and communities where there is a lack of regulated waste disposal and restrictions on the open burning of solid waste;
• Reduces pests and improves a community’s aesthetics near landfill sites;
• Improves the quality of urban and rural environments, particularly where improper MSW management contributes to flooding;
• Reduces the use of fossil fuels and concomitant production of GHG from trucks delivering MSW to distant landfill sites;
• Reduces the use of fossil fuels and concomitant production of GHG from equipment and machinery operating at landfill sites;
• Reduces significant GHG emissions (methane) from landfills as the waste is diverted from landfill;
• Produces a marketable byproduct in the form of fly and bottom ash that depending on the composition of the MSW can be sold as a soil conditioner, as a concrete strengthening and durability additive or as a liming agent in agriculture;
• Provides added revenue from the recovery of recyclable materials from the upstream MWS stream prior to conversion into the refuse derived fuel feedstock;
• Provides added revenues from carbon credits. An EnvirOcyler project can be registered under the United Nations clean development mechanism (CDM) to generate carbon credits for added revenue because its electricity generation offsets the equivalent quantity of carbon dioxide produced by electrical generation through the use of fossil fuels and also because managing MSW with the EnvirOcycler offsets the production of methane (a significant GHG) otherwise produced by the MSW if it were landfilled instead; and
• Creates employment opportunities for as many as 100 persons per 105 GJ EnvirOcycler unit.

Environmental Benefits

There are numerous environmental benefits associated with the use of the EnvirOcycler technology:

• reduced dependency on and displacement of expensive fossil fuels needed to generate grid power;
• avoidance of methane formation by diverting MSW from landfills;
• reducing the need for expanding landfills to accommodate growing volumes of MSW;
• estimated reduction of greenhouse gas emissions by over 50,000 tonnes CO2eq annually; and
• reducing risks of groundwater contamination from leachate through avoidance of MSW disposal at landfill sites.

Minimal Emissions

Some of the greater concerns of typical waste-to-energy projects are toxic emissions, more specifically dioxins and furans. AET/HPEG are very confident that toxic emissions will be insignificant on its EnvirOcycler projects due to the inherent design of the technology:

• Firstly, one needs to understand the conditions that are favorable for the formation of dioxins and furans: organic material that is being combusted is surrounded by air that is cooler than the combustion material leading to a combustion reaction that is incomplete. Uncombusted gases lead to formation of dioxins and furans. A good example of a reaction that emits a lot of dioxins and furans is a campfire or a forest fire;
• Within the EnvirOcycler unit, MSW is gasified in the first stage with the gases being transferred to a second stage for combustion;
• The surrounding air of the 2nd stage burner is very hot and contains an extremely vigorous intake of combustion air. The combustion air is taken into the chamber at “Mach I” speeds (i.e the speed of sound) causing a lot of swirling and “cyclonic vortexing” within the 2nd stage;
• The swirling and cyclonic vortex and the hot temperature of the 2nd stage do not allow dioxins and furans to form after the gas exits the 1st stage;
• As a safeguard to ensure no dioxins and furans are emitted, the AET/HPEG consortium will provide modern pollution controls including a bag house (to capture particulate matter) and an electrostatic precipitator (to washout any harmful chlorine gases or particulate matter that may be present after the heat goes past the 2nd stage).