POWER PRODUCTION \ WITH A ROTARY KILN INCINERATION LINE
Operating process of our WTP (Waste to Power) solution, a power plant operating with municipal waste and miscellaneous waste.
All types of wastes can be used, MSW or any other industrial waste, including specific wastes such as shredded tires, up to 25% of the total waste. All the collected waste is stored in transition silos. This waste is then subjected to a grinding operation with separation of the liquids, then it is eventually pre-dried. Liquid waste is injected into the combustion chamber using injectors for liquids (liquid, muddy, or pasty waste), which, like for solid waste, is done fully automatically after an operator has triggered loading, intrinsically safely.
The controls are made on a console which is installed near the machine, which allows a very clear vision of all stages of the different cycles. After starting up and heating the incinerator, all the machine cycles are then concurrent, i.e. all the cycles are in action, namely:
Taking over of the skips filled with waste at a specific location, the incinerator, by hydraulic assistance, transports these skips and empty them.
The waste, conveyed into the hopper, is then pushed into the combustion chamber. The loading is frontal with a «guillotine» door opens and closes after the introduction of this waste, which reduces heat loss during the introduction of waste.
For a rotary kiln, there is no mechanical stress because the furnace, made up of a tube, turns on itself. This tube has a degree of inclination calculated so that the waste remains inside the oven, and that it descends by gravity into the ash removal system. Waste is turned over during a descent whose time has been optimized, in order to guarantee better combustion and better elimination. It is at the end of this cycle that the ashes automatically fall into an extractor located under the furnace, which is also managed automatically.
Once the waste is incinerated and reduced to ashes, these ashes are extracted from the combustion chamber, the extraction is automatic and controlled by computer. The shutter is under the post combustion. This cycle is modular, this modulation will be done during the programming of the incinerator. Ashes represent around 2% to 3% of the weight of the loaded waste. The obtained ashes can be recycled in the civil works sectors, as an addition to bitumen for example.
This other cycle burns dust and other large particles inside the fumes. Burners are installed on this Post-Combustion to ensure proper operation and maximum elimination of these particles.
The quiet chamber
This chamber is designed and calculated according to the volumes of fumes to be treated and therefore also according to the quantity of waste to be destroyed. The fumes must remain in this confined space for at least 2 seconds at a minimum of 1100°C (European standards). A whole set of refractory concrete wall construction is installed inside, deviations and/or turns are used to slow down these fumes.
The cooling chamber (option)
This room comes after the quiet chamber, depends on the waste PCI, if the gases leaving the quiet chamber are still higher than 900°C.
With a robust design, this element has an important role for the following cycles. The heat exchanger has the role of lowering the smoke temperatures (depending on the kind of the waste) from 900°C-1000°C to around 100°C. If these temperatures at the outlet of the cooling chambers were not lowered, the following cycles which are the injection of lime and activated carbon into a dilution reactor, and above all the filtration system would be highly disturbed and damaged. These cycles which ensure emissions with a minimum of pollutants would be totally ineffective. The heat exchanger is the element from which a heat transfer fluid loop is created which either brings the heat form the hot fumes to the coolers in order to cool the fumes so that they can be treated, or feeds the ORC with that heat, which in this case will ensure at the same time the functions of cooling the fumes and electricity production.
The ORC (Organic Rankine cycle) works like a usual Rankine cycle, just like the steam cycle does, but the water is replaced by an organic fluid, called working fluid, which has the particularity of having a boiling point much lower than the water. You can see the ORC cycle described in the diagram above. This working fluid, passing through the evaporator, is vaporized by the heat sent from the heat exchanger (thermal oil loop). This fluid, in a vapor phase, turns a turbine which drives a generator (working fluid loop), that is where the production of electricity takes place. Then the working fluid is re-condensed in a liquid phase by the condenser which is connected to the coolers (cooling water loop). To end the cycle, a pump returns the working fluid in a liquid phase to the evaporator. The process restarts repeatedly. All these loops are completely closed, and therefore, there is no fluids consumption.
The dilution reactor
The injection of hydrated lime to neutralize acids (HCL, SO2, HF) and the injection of activated carbon to absorb furans and dioxins (2 separate hoppers are provided for this purpose) are used to capture the residues in the fumes and to weigh them down. Located between the heat exchanger that cools the fumes and the filtration system that filters the same fumes, the reactor is made up of piping for transporting and above all reducing the temperatures of the treated fumes to the filtration system. This processing is compulsory. The size of this reactor is also proportional to the quantity of the fumes to be treated and therefore to the quantity of waste to be incinerated.
There are many filtration systems. The one we use in our power plants incinerators is the ceramic candle filter. These filters are reliable and do not require any particular maintenance, only preventive maintenance is required. On one hand, these filters capture harmful fumes through ceramic candles, and on the other hand, they collect the dust in a hopper provided for this purpose. This cycle does not require any human intervention. A calculated and proportioned compressed air jet ensures this operation automatically.
With a standard height of around 20 meters, it can be higher according to the standards of each country. Generally, made of 304L stainless steel, it is mechanical welded and is held by a steel frame.
The exhausts fan
Its power varies according to the quantity of waste to incinerate. This fan will suck the fumes from the combustion chamber and all along the line. It will drive and force the fumes towards the chimney.