Business Strategy Division, R&D Center
Resource Recycling Technology Development Department
Naoto Watanabe
Saving energy is a big challenge at wastewater treatment facilities, especially during sludge incineration processes that requires a large amount of electricity.
Our newly developed fluidized turbine system can cut down on the electricity consumption of the fluidized incinerator by approximately 40% without compromising safety, security, or stability.
This is also an innovative technology that can be introduced within existing facilities with partial renovations taking place.
We had an interview with Naoto Watanabe, who led the project, regarding the advantages of the technology and the background behind the development.
The sludge produced during wastewater treatment, goes through concentration, digestion, and dehydration processes and is then sent to a fluidized incinerator, where it is incinerated at a high temperature of 850°C. To maintain an ideal combustion state during incineration, air is constantly blown into the layer of sand at the bottom of the furnace by a fluidized blower to form a fluidizing state. To press air into the sand layer, a large discharge pressure is required of the blower, leading to increased power consumption. It used to be as much as 40% of the entire incineration system.
I wondered if we could cut down on the total power consumption of the fluidized blower by replacing it with a new alternative system. Development was triggered by such motivation.
“A supercharger will be used instead of fluidized blower. In addition, we will establish our own unique system.” The direction of development was clear from the beginning. However, we had never operated a supercharger before and had no knowledge about it or know-how related to it. Therefore, what we did first was purchase a turbocharger for cars and started testing it. It didn’t take long until we realized that operating a turbocharger was not as easy as we had thought. Blowers are easier to use because the discharge pressure increases slowly. A turbocharger, however, consisting of a compressor to compress air and a turbine that rotates due to the expansion of the compressed air, cannot be controlled in the same way. It was difficult to control the heat going to the turbine while changing or maintaining combustion air amounts while seeing fluctuations take place in terms of collected discharge heat amounts. To control it, we had to repeatedly experiment, collect experiment data, and keep adjusting things. We were asking ourselves how fast we should make the air supply. We were also asking ourselves at which point should we be sending it faster and from which point should we be sending it slower. We found the optimum switch points and were successful in making the pressure changes more stable. Our days were like a seesaw. We discussed and shared ideas among the team, and experimented with those ideas.
We turned the technology into a reality through such painstaking labor.
The completed fluidized turbine system turns the turbocharger using waste heat produced by combustion and supplies combustion air to the fluidized incinerator.
(1) A turbocharger installed in the combustion supply line compresses air.
(2) Compressed air is heated by pre-heaters and resupplied to the turbocharger.
(3) The air that passed through the turbocharger is sent to the incinerator as combustion air.
This cycle is repeated.
●Approximately 40% of electric power is saved
Instead of using a fluidized blower, a turbocharger is driven through the utilization of waste heat produced by combustion, achieving approximately a 40% cut in power consumption in the incineration system.
●厂补蹿别
As with the conventional system, the fluidized incinerator and the combustion exhaust gas line have a negative pressure.
Thus, the risk of exhaust gas leakage is extremely low.
●厂别肠耻谤别
The only change from the conventional system is the combustion air supply method.
It offers the same secure sludge treatment as before.
●厂迟补产濒别
The air that drives the turbocharger is clean.
There is no need to worry about damaging the turbocharger with dust.
●Can be introduced with partial modification to existing facilities
The existing facilities can be utilized. Only a turbocharger and the replacement of pre-heaters are required. Another advantage, is that it can be introduced easily at the time of pre-heater replacement.
Of course, it can be introduced not only within general fluidized incinerators but also within circulating fluidized incinerators or multi-layer fluidized incinerators. It can be introduced in various systems regardless of their scales.
Although we found things to be incredible tough each day, we were able to accomplish the development of our fluidized turbine system because we were driven by the passion to succeed in dramatically cutting the power consumption by replacing the fluidized blower with a turbocharger. I think this technology still has huge hidden potential. Controls can be further explored.
In the future, I want to take the advantage of my experience and promote power generation using waste heat . I hope in the end, that we will be able to cover all the electricity used for the entire sludge incineration system with generated power.
Lastly, clues may be all around us and found in unexpected places. That’s why we need to keep ourselves open to information found in various fields and increase the opportunities we have to learn. What really counts is how we think up new ideas, sort them out, and how we make them come true. That’s the mission of developers.
Business Strategy Division, R&D Center
Resource Recycling Technology Development Department
Engaged in the development of sludge treatment facilities since joining the company.
Engaged in innovation for processes in general, including fluidized incinerators and sludge-gas conversion technologies.
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