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Data Entry: June 2011
Name of Technology Production of Activated Carbon from Sewage Sludge and Cost Reduction of Sludge Treatment by Effective Utilization
Technology Owner Kawasaki Heavy Industries, Ltd.
Kimura Manufacturing Co., Ltd.
General Description This technology aims to encourage the recycling of sewage sludge by producing activated carbon from sewage sludge via drying, carbonization and activation processes that create a micropore structure, and by encouraging the use of the activated carbonized products.
Another goal of this technology is to implement it at small wastewater treatment plants as well, by modularizing the activated carbon production technology so that it can be assembled at users Eplants at lower cost.

Components of Technology The system comprises the following three main equipment components.
[1] Dryer module: Drying unit and its ancillary equipment for drying dewatered sludge
[2] Carbonizing furnace module: Externally heated carbonization-activation screw unit and its ancillary equipment for producing activated carbonized products from dried sludge
[3] Heat recovery device: Heat exchanger for recovering heat from the combustion gas produced by the carbonizing furnace module and transferring the recovered heat to the circulating dryer exhaust produced by the dryer module






Flowchart of activated carbonization


Dewatered sludge is converted into activated carbonized products through the processes shown below.
Dewatered sludge is fed to the drying unit in the dryer module via a sludge pump and is dried to a moisture content of 10% to 20%. (Drying process)
The dried sludge is then fed to the carbonization-activation unit in the carbonizing furnace module.  In the screw casing which is heated to a high temperature, the dried sludge undergoes carbonization in the front section and then activation in the rear section, becoming activated carbonized products. (Carbonization-activation process)
The present system produces dryer exhaust from the dryer module and combustion exhaust from the carbonizing furnace module. The dryer exhaust is divided into circulating dryer exhaust and excess dryer exhaust.
These gases flow as follows.
The excess dryer exhaust is cleaned by the scrubber, undergoes a hot deodorization process in the carbonization-activation unit, and is released to the atmosphere with combustion gas.
The circulating dryer gas returns to the dryer module after being heated by the combustion exhaust in the heat recovery device.
Features of Technology 1. System Features
(1) Reduced construction cost
When modularized for assembly at the user's plant, the three main equipment components can substantially reduce the construction cost.
(2) Reduced operating cost
The following three features of the system raise the total thermal efficiency and thus reduce the operating cost.
  • [1] Water evaporating from sludge (steam) is used as a heating medium to reduce the volume of dryer exhaust.
  • [2] Dryer exhaust is introduced to the carbonizing furnace for deodorization, thus eliminating the need for a deodorizing furnace.
  • [3] Heat is recovered via heat exchange between the dryer exhaust and carbonizing furnace exhaust.

The dryer exhaust is steam evaporating from dewatered sludge. By using the steam as a heating medium for recovering heat from the hot combustion gas via the heat recovery device, thus eliminating the need for a hot-air source required by the conventional drying unit, the system improves the thermal efficiency and reduces the operating cost.
Moreover, since the steam concentration of the excess dryer exhaust is extremely high, heat loss is minimal during cleaning by the scrubber, and so the volume of excess dryer exhaust that requires hot deodorization is minimized.
The system also reduces the volume of combustion exhaust, minimizes heat loss from the combustion exhaust, and improves the total thermal efficiency. This energy saving helps mitigate global warming.

2. Features of Carbonization-Activation Process
Activation imparts adsorption activity to carbonized sludge. Chemical energy equilibrium calculations suggest that this reaction occurs at 800°C or more and not at about 600°C. The present technology ensures that the temperature difference between the material in the screw conveyor and the exhaust serving as a heat source is 100°C or less, because the inside surfaces of the heat-exchange steel sheet are constantly refreshed by the screw which prevents the deposition of scale. Accordingly, by controlling the combustion gas temperature in the material activation section to 900°C or higher, the material can be heated at a temperature above 800°C. In this high-temperature reducing atmosphere, micropores grow as a result of the activation reaction between carbonized material and steam and the like. The carbonization-activation process of the present technology has the following features:

  • [1] Performs carbonization and activation processes continuously in a single furnace.
  • [2] Retention time is easily controlled by the rotational speed of the screw in the carbonizing furnace.
  • [3] The screw conveyor prevents the deposition of scale inside the conveyor.
  • [4] Granular dried sludge 1 mm or less in particle size ensures efficient heat transfer.
  • [5] The stable activation reaction atmosphere achieved by an externally heated system produces high-quality activated carbonized products.
  • [6] The steam and carbon dioxide gas generated from sludge are used as activation gases.

1.3.3 Product Features
The product has the following features.
(1) Adsorbent
[1]Adsorptivity: The product can be used as a dioxin adsorbent and deodorizer due to its large specific adsorption surface area.
[2]Safety: The product's high ignition temperature of 300°C makes it safe to handle during storage and transportation.(2) Coagulant
[1]Cohesiveness: The product has high coagulation effects due to its high heavy metal contents in a reduced state.
[2]Settleability: The product exhibits good settleability due to its high specific gravity.

Properties of activated carbonized products

 Item  Range
 Ignition loss  30 to 55%
 Bulk density  0.4 to 0.8
Average particle size  100 to 300 μm
 Ignition temperature  300 to 400°C
 Fixed carbon  20 to 50% (DS)
 Atomic H/C ratio  <0.2
 Specific surface area  50 to 150 m2/g (150 to 600 m2/g-carbon)
 Average micropore diameter  20 to 60 ÁE/td>



Activated carbonized product and its microphotograph

Evaluation of Technology

This technology was developed in the LOTUS Project (Lead to Outstanding technology for Utilization of Sludge Project) and evaluated and reviewed by the Sewerage Technology Development Project Committee under the Ministry of Land, Infrastructure and Transport in Japan in 2007. 

[Link to the technology evaluation report]

Note: This technology was developed by Kawasaki Environmental Engineering Co., Ltd. and Kimura Manufacturing Co., Ltd., and evaluated in 2007. Kawasaki Environmental Engineering Co., Ltd. has been consolidated into Kawasaki Heavy Industries Ltd. since 2010.

Contact Information Industrial Plant Sales Department (Chemical Plant), Plant & Infrastructure Company,
Kawasaki Heavy Industries
Ltd.
URL: http://www.khi.co.jp/english/kplant/business/environment/water/dirt.html
For inquiry: http://www.khi.co.jp/cgi-bin/other-q1_e.cgi?form-type=ind-plant&ca_no=30

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