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AUTOCLAVING
Feb 25th, 2010 by 20073103

Autoclaving involves the high-pressure sterilisation of waste by steam, which ‘cooks’ the waste and so destroys any bacteria in it. This process is widely used to treat clinical waste, but is increasingly being proposed as a treatment for municipal waste. The process creates a so-called ‘fibre material’ from the biodegradable portion of the waste, which is separated along with some recyclable materials. Although there are no facilities operating commercially to treat municipal waste in the UK, there are several plants being built or planned. There are currently no clear markets for this ‘fibre material’, which will consist of a wide range of materials e.g. food, paper etc. This material would also still biodegrade if landfilled, so would require further treatment (e.g. composting) prior to landfill. It is therefore likely that much of the output from autoclaves will end up being be burnt as ‘refuse derived fuel’.

How autoclaving works

Autoclaving of municipal waste is a form of ‘mechanical heat treatment’ (MHT) – a process that uses thermal treatment in conjunction with mechanical processing.

Waste may initially be screened for the removal of any large items, and possibly shredded. The unsorted waste is sealed in an autoclave, which is a large, enclosed vessel about the size of a long fuel tanker that rotates to agitate and mix the waste.

Using the ‘pressure cooker’ principle, steam is injected at pressure – raising the temperature up to 160°C (degrees centigrade). The pressure is maintained for between 30 minutes and one hour. This sterilises the waste, by destroying bacteria present. It reduces the volume of waste by about 60 per cent, and reduces the moisture content.

The cellulose in all the organic matter – the biodegradable waste including food and garden waste, paper and card – is broken down into a ‘mush’ of fibre, sometimes know as floc or fluff.

After autoclaving, the waste is discharged and processed by mechanical separation technologies, similar to those used in MBT systems. Metals will be extracted for recycling, and possibly also plastics for recycling and glass for re-use as aggregate. There is a residue or ‘reject fraction’ that needs to be landfilled.

Typical outputs are:

64% ‘organic fibre’

17.5% recyclables

2.5% aggregate

16% other materials suitable for landfill

9% mixed plastics

4% glass

3.5% steel

1% aluminium

The water used in the process will usually be trapped and recycled, and wastewater will be discharged as an effluent stream, which removes pollutants from the process.

PYROLYSIS
Feb 23rd, 2010 by 20073103

Pyrolysis is the thermal degradation of a substance in the absence of added oxygen. The general characteristics of pyrolysis of a waste stream are as follows:
1)    No oxygen is present (or almost no oxygen) other than any oxygen present in the fuel;
2)    Low temperatures typically from 300 °C to 800 °C;
3)    Products are syngas (main combustible components being carbon monoxide, hydrogen,
methane and some longer chain hydrocarbons including condensable tars, waxes and oils)
and a solid residue (consisting of non-combustible material and a significant amount of
carbon);
4)    The general lack of oxidation, and lack of an added diluting gas, means that the NCV of syngas from a pyrolysis process is likely to be higher than that from a gasification process (provided substantial quantities of carbon are not left in the solid residues). Typical NCV for the gas produced is 10 to 20 MJ/Nm3;
5) The overall process generally converts less of the chemical energy into thermal energy than gasification. Pyrolysis also offers the potential option of more innovative use of the pyrolysis syngas other than immediate combustion to produce heat. Pyrolysis generally takes place at lower temperatures than for combustion and gasification. The result is less volatilisation of carbon and certain other pollutants such as heavy metals and dioxin precursors into the gaseous stream. Ultimately, the flue gases will need less treatment to meet the emission limits of WID. Any pollutant that is not volatilised will be retained in the pyrolysis residues and need to be dealt with in an environmentally acceptable manner. The emission benefits of low temperature processing are largely negated if the char subsequently
undergoes high temperature processing such as gasification or combustion.
The solid residues from some pyrolysis processes could contain up to 40% carbon representing a significant proportion of the energy from the input waste. Recovery of the energy from the char is therefore important for energy efficiency.

Gasification is the partial thermal degradation of a substance in the presence of oxygen but with insufficient oxygen to oxidise the fuel completely (i.e. sub-stoichiometric). The general characteristics of gasification of a waste stream are as follows:
1)    A gas such as air, oxygen, or steam is used as a source of oxygen and/or to act as a carrier
gas to remove the reaction products from reaction sites;
2)    Moderate temperatures typically above 750 °C;
3)    Products are gas (main combustible components being methane, hydrogen, and carbon
monoxide) and a solid residue (consisting of non-combustible material and a small amount of carbon);
4)    The overall process does not convert all of the chemical energy in the fuel into thermal energy but instead leaves some of the chemical energy in the syngas and in the solid
residues;
5)    The typical NCV (net calorific value) of the gas from gasification using oxygen is 10 to 15 MJ/Nm3;
6)    The typical NCV of the gas from gasification using air is 4 to 10 MJ/Nm3.
For comparison, the NCV for natural gas is about 38 MJ/Nm3.

Gasification offers at least the theoretical potential for innovative use of the product syngas other than immediate combustion to produce heat. Examples of innovative use would be firing of the syngas in gas engines/turbines, the displacement of fossil fuel in large combustion plants or as feedstock for chemicals or liquid fuel production.

SALT WATER
Feb 11th, 2010 by 20073106

You may have heard about an invention created by a 63-year-old named John Kanzius that claims to create an alternative fuel out of salt water. Through sheer serendipity, Kanzius, a former broadcast engineer, found out something incredible — under the right conditions, salt water can burn at high temperatures.

Kanzius’ journey toward surprise inspiration began with a leukemia diagnosis in 2003. Faced with the prospect of debilitating chemotheraphy, he decided he would try to invent a better alternative for destroying cancerous cells. What he came up with is his radio frequency generator (RFG), a machine that generates radio waves and focuses them into a concentrated area. Kanzius used the RFG to heat small metallic particles inserted into tumors, destroying the tumors without harming normal cells.

But what­ does cancer treatment have to do with burning salt water?

During a demonstration of the RFG, an observer noticed that it was causing water in a nearby test tube to condense. If the RFG could make water condense, it could theoretically separate salt out of seawater. Perhaps, then, it could be used to desalinize water, an issue of global proportions. The old seaman’s adage “Water, water everywhere and not a drop to drink” applies inland as well: Some nations are drying up and their populations suffering from thirst, yet the world is 70 percent ocean water. An effective means of removing salt from salt water could save countless lives. So it’s no surprise that Kanzius trained his RFG on the goal of salt water desalinization.

During his first test, however, he noticed a surprising side effect. When he aimed the RFG at a test tube filled with seawater, it sparked. This is not a normal reaction by water.

Kanzius tried the test again, this time lighting a paper towel and touching it to the water while the water was in the path of the RFG. He got an even bigger surprise — the test tube ignited and stayed alight while the RFG was turned on.

News of the experiment was generally met with allegations of it being a hoax, but after Penn State University chemists got their hands on the RFG and tried their own experiments, they found it was indeed true. The RFG could ignite and burn salt water. The flame could reach temperatures as high as 3,000 degrees farenheit and burn as long as the RFG was on and aimed at it.

But how could salt water possibly ignite? Why don’t careless litterbugs who flick lit cigarette butts into the sea set the whole planet aflame? It all has to do with hydrogen. In its normal state, salt water has a stable composition of nacl (the salt) and hydrogen and oxygen (the water). But the radio waves from Kanzius’ RFG disrupt that stability, degrading the bonds that hold the chemicals in salt water together. This releases the volatile hydrogen molecules, and the heat output from the RFG ignites them and burns them indefinitely.

So will our cars soon run on salt water instead of gasoline?

Aquygen

Since the oil crisis of the 1970s revealed the danger of our dependence on fossil fuels, chemists,engineers,physists and charlatans alike have tried to come up with alternatives. In this search, John Kanzius is not the first to come up with water as a potential fuel. In 2006, a company out of Clearwater,  called Hydrogen Technology Applications debuted Aquygen, a gas made up of hydrogen separated from water through an electrical shock. This hydrogen gas, when mixed with regular gasoline, creates a more efficient fuel than gasoline alone by burning what is normally emitted as waste and using it for power. HTA’s president, Denny Klein, claims the mixture improves gas mileage by as much as one-and-a-half times and reduces pollution

Klein created a hybrid vehicle out of a 1994 ford Escort. This vehicle used electricity from the alternator to create the impulse needed for hydrogen separation. It then sent the gas into the fuel tank for mixing. But while the hydrogen gas produced was fuel-efficient, it was also highly volatile, meaning it could easily explode.

There is another design flaw in Aquygen, one that it shares with the Kanzius RFG. Both struggle with the energy input to energy output ratio — or efficiency. This huge stumbling block causes many to view inventions like Aquygen and the RFG as useless science. While the RFG produces a hydrogen flame that burns stably, the amount of energy it puts out is less than the amount of energy needed to power the RFG. In this sense, any energy that comes out of the salt-water flame cannot be considered a source of power. It’s just a manifestation of the energy being put into it, only in a lesser amount. This makes it unlikely that the RFG could produce a real, viable source of fuel.

Just about any electrical or chemical process puts out some kind of energy, for example, in the form of heat. In power sources, the goal is to create more energy than is used in the process. Once you consider how few sources of energy can produce more energy than their process requires, the difficulty of such a quest, and the maddening frustration that accompanies it, becomes clearer. It’s a little like alchemy — the quest to turn ordinary metals into precious ones.

But it’s encouraging that Penn State chemists experimenting with the RFG discovered that Kanzius’ process produces different amounts of heat energy from different salt water concentrations. Perhaps the answer to the energy ratio lies in the amount of salt. Another hopeful sign is that the process doesn’t require sea water; it works with salt added to fresh water, too. If we use salt water as fuel in the future, landlocked nations wouldn’t find themselves battling coastal countries for it.

Like Isaac and his falling apple, or Alexander Flemming and his accidental penicillin spores, John Kanzius stumbled onto his discovery. But unlike Newton and Fleming, Kanzius is yet to be validated by history. Until the energy input versus output ratio can be overcome — if, indeed, it can — Kanzius’s exciting discovery will remain just that: an exciting discovery. But with a major university behind it, Kanzius’s RFG isn’t down for the count. The RFG’s inventor can also look forward to further research into other applications for his machine.

»  Initiated by Virupakshan of www.HomePlanGuru.com
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