Incineration

Incineration  MSW is burnt in a properly designed furnace under suitable temperature and operating conditions. This process is called as incineration.  It is one of the most effective method of reducing the volume and weight of municipal solid waste.  The process consists of controlled burning of waste at high temp (1200- 1500°C).  It sterilizes and stabilizes the waste with reduction in the volume.

Incineration  It is a process in which carbon, hydrogen and other elements in the waste mix with oxygen in the combustion zone and generates heat. This reaction is called as oxidation.  For complete oxidation the waste must be mixed with appropriate volume of air. Approx. 5000kg of air is required for each tone of solid waste burned. It differs with moisture content, heating values of waste and type of combustion .  Proper temp must be maintained for suitable length of time.

Incineration Process

Incineration Process

Incineration  The process can reduce MSW by about 90% in volume and 75% in weight.  Temperature ensures good combustion and complete elimination of odour.  The combustion process is based on 3T’s Time Temperature Turbulence (gas velocity)

Objectives of Incineration 1. Volume Reduction- To combust SW to reduce their volume to 1/10th without producing offensive gases and ash.  Volume reduction depends upon the MSW composition. General volume reduction is by 90% and weight by 75%. 2. Stabilization of waste– output from incinerator is more inert than input due to oxidation of organic components of waste stream.

Objectives of Incineration Recovery of energy from waste – Energy recovered from burning of waste is used to generate steam for on site electricity generation or export to local heating schemes. Combined heat and power plants increase the efficiency of energy recovery by producing electricity as well as utilizing residual heat. It reduces demand on fossil fuels. Sterilization of waste– Important for incineration of clinical/biomedical waste. It ensures pathogen destruction prior to final disposal.

Advantages of incineration  The volume and weight of the waste are reduced to a fraction of its original size.  Waste reduction is immediate, does not require long term residence.  Waste can be incinerated on site without carted to a distant area.  Air discharge can be effectively controlled for minimal impact on the atmospheric environment.

Advantages of incineration  The ash residue is usually non putrescible or sterile.  Technology exists to completely destroy even most hazardous material in a complete effective manner.  Requires relatively small disposal area compare to land burial. Particularly popular in countries such as Japan where land is a scarce resource.  By using heat recovery techniques the cost of operation can often be reduced or offset through the use or sale of energy. (resource recovery/ waste to energy facility)

Advantages of incineration Denmark and Sweden have been leaders in using the energy generated from incineration for more than a century, in localized combined heat and power facilities supporting district heating schemes. A number of other European countries rely heavily on incineration for handling municipal waste, in particular the Netherlands, Germany and France.

Disadvantages of incineration  The capital cost is high.  Skilled operators are required.  All materials are not incinerable (construction and demolition waste).  Supplemental fuel is required to initiate and at times to maintain the incineration process.  The most publicized concerns from environmentalists about the incineration of municipal solid wastes (MSW) involve the fear that it produces significant amounts of dioxin and furan emissions.

Disadvantages of incineration The solid residue remaining in the furnace after incineration is called as bottom ash which ultimately go for land disposal. The bottom ash may contain metals like lead and cadmium, can be treated prior to disposal. Dioxins occur as in the incineration of chlorine-containing substances such as PVC (polyvinyl chloride)  Health effects such as Developmental of abnormalities in the enamel of children's teeth. Central and peripheral nervous system Thyroid disorders Damage to the immune systems Endometriosis Diabetes

Disadvantages of incineration  Fly ash is the incinerator ash carried along in the combustion airstream. So air pollution control devices are installed to remove fly ash and potentially harmful gaseous contaminants.  Thus, Installation of air pollution control equipment make the process expensive.  These equipments are located after the furnace and before the stack.

Important Factors For Incineration waste moisture content– The greater the moisture content , more fuel is required to destroy the waste. Heating Value–With no significant heating value incineration would not be a practical disposal method.

Important Factors For Incineration Inorganic salts– waste rich in inorganic, alkaline salts are troublesome to dispose of in a conventional incineration system. A significant fraction of the salt get collected on furnace surface, creating a slag or cake which severely reduces the ability of an incinerator to function properly. High sulfur or halogen content– The presence of chlorides or sulfides in waste will normally result in the acid forming compounds in the off gas.

Pyrolysis

Pyrolysis  Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures in the absence of oxygen.  It involves the simultaneous changes of chemical composition and physical phase, and is irreversible.  Pyrolysis is a type of thermolysis and is most commonly observed in organic materials exposed to high temperature.

Pyrolysis  Pyrolysis of organic substances produces gas and liquid products and leaves solid residue richer in carbon content, char.  Pyrolysis is used heavily in the chemical industry for example to produce charcoal, activated carbon, methanol and other chemicals.  It is also a tool of chemical analysis, for example in mass spectrometry and in carbon-14 dating.

Pyrolysis  Pyrolysis occurs whenever food is exposed to high enough temperatures in a dry environment such as roasting, toasting or grilling, baking, frying, grilling and caramelizing.  In normal cooking, the main food components that undergo pyrolysis are carbohydrates (including sugars, starch, and fiber) and proteins.  Pyrolysis of fats requires a much higher temperature and it produces toxic and flammable products.

For agricultural waste typical temperature range is 450º-550º C. Pyrolysis In many industrial applications, the process is done under pressure and at operating temperatures above 430º C. For agricultural waste typical temperature range is 450º-550º C.

Pyrolysis