The Hampshire, UK-based company PyroPure has developed a small-scale on-site thermal treatment unit intended, at least initially, for offensive wastes.
At around the size of a chest freezer the system almost fits into the category of domestic appliance. That makes it ideal for the nursing and care homes, which will provide a substantial initial focus for the company. The system features a 100 litre chamber, which is enough for around two regular bin bags of waste. To treat the waste it uses both pyrolysis, in which the waste is heated in the absence of oxygen and gasification where the waste is processed in the presence of very little oxygen. PyroPure’s system is capable of transforming 6kg to 12kg of any type of organic waste into just a handful of residue, while recovering more energy in the form of heat than processing the waste uses. What happens to this waste heat is not explained though it appears from the companies web site that this may be recovered within the treatment process with excess dispersed to atmosphere.
This sounds interesting, and may be applicable to other controlled waste streams, though the size is considerable and the two bag limit – compression would be inappropriate – will limit throughput. The location of such a device in a small nursing home, clinic or other healthcare establishment may be an issue, with hookup for power, water and drainage. Noise may also be a problem if it causes disturbance to patients and others. The residues require disposal, creating an additional cost and some concern over the regulatory status of effluents. and residues.
The main problem may be capital and other costs, that would be high for the occasional processing of just 2 bags of offensive waste. In all probability, other markets must be identified to make best use of this small throughput and possibly substantial cycle times.
How it works
The system features a 100 litre chamber, which is enough for around two regular bin bags of waste. To treat the waste it uses both pyrolysis, in which the waste is heated in the absence of oxygen and gasification where the waste is processed in the presence of very little oxygen.
“We heat the chamber up to around 500°C- 600°C and all the organic waste vaporises, primarily into CO, and we then put that gas through a catalytic converter, which at around 400 degrees will convert the CO and other tars and polluting gases into clean CO2. We then put that hot clean gas through a heat exchanger to recapture all the heat energy, both the input energy and the chemical energy in the waste and convert that into hot water which we can export from the machine. We can export more energy than we use to run it,” explains PyroPure.
Finally there is a scrubbing process that scrubs any acidic components such as hydrogen chloride that might come from plastics.
The system uses a water type scrubber that has a very fine mist of water that reacts with the acidic component in the gas as the gas rises and the water falls. The water used in the process is periodically flushed to the sewage system, as is the solid residue from the waste. However, the quantity of residue discharged is small.
According to PyroPure, the system has the capacity to process around 15 tonnes of waste per year, with less than 300kg of residue remaining to be discharged. If inorganic materials such as glass, metals and ceramics are mixed with organic materials in the chamber they are not destroyed, but are cleaned and sanitised and safe to be sent for recycling.
With regard to permits, PyroPure says that for the field trials the company always secures a Consent to Discharge from the local water authority. PyroPure is currently discussing whether that will be necessary for commercial deployment of the machine, but is working on the assumption that it will be -although it has not been a problem to date.
In terms of energy recovery, because the system operates on a batch process and the machine is not running continuously, the company found that the most efficient means of using the heat is to provide a preheated water supply for an existing boiler system. This means that the boiler is not taking cold water from the mains at 12°C or 13°C, but taking it at 30°C to 40°C.
In order to ensure that the waste material is fully treated the machine utilises a software system that allows for variations in the waste stream. The software – developed in house by PyroPure – controls the heat going into the primary chamber and speeds the process up or slows it down depending on how much energy is in the waste stream. It also monitors the amount of water present in the waste and adapts the cycle accordingly, as well as measuring and recording the exit gases.
According to PyroPure, the software is one of the most crucial aspects of the system and offers a host of safety features that will safely shut the machine down should certain parameters be breached. The key to it is that it’s very much plug and play, so a nurse in a care home can load the machine, lock the lid and come back four hours later with no operator intervention required.
Four hours, to process 2 bags of offensive waste seems an astonishingly slow and inefficient process, and that may be the Achilles heel of what otherwise seems like an exciting product development.