Kalogeo Technology

Increasingly restrictive regulations governing sewage sludge management are forcing a shift away from existing recovery and disposal methods based on natural (agricultural) use. Furthermore, starting in 2013, depositing sludge in landfills will be prohibited. The most promising solution appears to be the thermal conversion of sludge with thermal energy recovery, which is a renewable source.

Sludge drying is merely a half-measure. In most EKOTOP-designed drying plants, although the dried sludge (granulate) is reduced in quantity by more than half compared to mechanically dewatered sludge, it is still managed agriculturally.

It must be emphasized that dried sludge, in accordance with national regulations, cannot be treated as biomass and incinerated in conventional boiler houses.

Definitions of biomass are contained in two legal acts: the Regulation of the Minister of the Environment of December 20, 2005, on emission standards from installations (Journal of Laws No. 260, item 2181, as amended), and the Regulation of the Minister of Economy of August 14, 2008, regarding the detailed scope of obligations to obtain and present for cancellation certificates of origin, payment of the substitution fee, purchase of electricity and heat generated in renewable energy sources, and the obligation to confirm data regarding the amount of energy generated in a renewable energy source (Journal of Laws No. 156, item 969).

The two definitions differ. In both cases, biomass includes both certain products and certain wastes. It should be emphasized that classifying waste as biomass is not a criterion that determines it ceases to be waste. Indeed, biomass also includes certain wastes, the incineration of which requires a permit for waste recovery or disposal operations, as referred to in Art. 26 of the Waste Act.

Citing §5 sec. 6 of the Regulation of the Minister of the Environment on emission standards from installations, fuel is any solid, liquid, or gaseous substance, with the exception of waste, whereby biomass is also considered fuel, understood as:

  • Products consisting wholly or partly of vegetable matter from agriculture or forestry, incinerated to recover the energy content thereof.

  • The following wastes:

    • Vegetable waste from agriculture and forestry;

    • Vegetable waste from the food processing industry, if the heat generated is recovered;

    • Fibrous vegetable waste from virgin pulp production and from the production of paper from pulp, if it is co-incinerated at the place of production, and the heat generated is recovered;

    • Cork waste;

    • Wood waste, with the exception of wood waste that may contain halogenated organic compounds or heavy metals as a result of treatment with wood preservatives or coating, and which includes, in particular, such wood waste originating from construction and demolition waste.

Therefore, from the perspective of emission standards, dried sludge cannot be treated as biomass, as it does not meet the definition of biomass set out in the aforementioned regulation on emission standards from installations. It must still be treated as waste within the meaning of the Waste Act, and installations used for the thermal conversion of sludge must meet all requirements specified in the regulations (including emission standards) for waste incineration or co-incineration plants.

Since the commissioning of the first solar sludge-drying plant designed by EKOTOP, we have been inundated with inquiries about the further management of dried sludge. Currently, in cooperation with the Austrian company KALOGEO, our offer includes sludge incineration plants capable of incinerating both dried sludge (mechanically dewatered) and other organic waste, e.g., screenings. This installation has appropriate safeguards that ensure no negative impact on the environment.

Case Study: Incineration Plant in Bad Vöslau (Austria)

The complete installation consists of a solar-type drying plant and an incineration plant. It serves a wastewater treatment plant generating approximately 14,000 Mg of sludge annually (after dewatering on a chamber press) with an average dry matter content of 24%. From under the press, the sludge is loaded via a screw conveyor system into containers, which transport it to a complex of 4 solar drying halls, where it is pre-dried to approximately 45% dry matter. The heat generated by the sludge incineration process assists in drying during winter periods; therefore, the solar dryers operate at full capacity in a year-round system. Additional excess heat powers the local boiler house, supplying heat for the town of Bad Vöslau.

The fact that solar dryers are used does not mean they are an inseparable element of the incineration plant. It is possible to use other types of dryers, allowing for the pre-drying of sludge to the required 45% dry matter. One proposal is a belt dryer that can utilize hot oil (210°C at the inlet) from heat exchangers in the sludge incineration installation. Such a dryer operates at a slight negative pressure, and emissions generated in the drying process are returned to the furnace via a fan and incinerated.

Pre-dried sludge is loaded by a front loader into the common hopper of a screw conveyor located at the end of the solar drying halls, from where it is transported by a system of vertical and inclined feeders directly to the KALOGEO incineration installation.

The dried sludge is fed to the pre-storage tank of the fluidized bed furnace via a chain conveyor. The dosing system consists of a rectangular, open silo with a capacity of 3 m³ and spiral conveyors for material dosing. Next, the sludge is fed via a conveyor belt to a feeding aggregate located in the furnace reactor. This aggregate distributes the sludge evenly on the bed. The installation has an additional hopper enabling the feeding of screenings or other organic waste into the furnace.

The Incineration Process

The furnace reactor is essentially a steel container filled with quartz sand. Cold air distributors are located at the bottom of the bed, through which air is introduced into the bed. The air flowing from below fluidizes the sand layer, giving it liquid-like properties. The most important properties of the fluidized bed installation are uniformly constant temperature, intensive mixing of components, and good "heat transfer."

Water contained in the sludge evaporates, and organic components gasify. Gas products rise to the surface of the bed where they are immediately incinerated. The combustion energy is absorbed by the quartz sand in the bed, and as a result, the amount of natural gas introduced into the system at the moment of "start-up" can be reduced to level "0". Gases in the reactor above the bed (in the freeboard area) remain for the statutory minimum of 2 seconds at a temperature of a minimum 850°C.

The gas combustion temperature is maintained at the inlet to the heat exchanger below 850°C. This occurs using external air and gases generated in the drying process. Heat is transferred in the heat exchanger to the oil system and discharged to the drying installation. Excess heat generated during the drying process is cooled with water.

In the next stage, gas cleaning is conducted using a centrifugal separator (cyclone), the primary function of which is to reduce dust levels in the gas. This dust is discharged through a "rotary valve" (airlock) and a screw conveyor, then transported to the filter. The centrifugal separator is a steel construction with inspection openings in the cone, necessary static supports, and other accessories, and is protected against wear by a protective layer of a special compound.

In the dry sorption process, the concentrations of HCl, HF, and SO₂ in the gas are reduced by introducing lime/sodium bicarbonate and active coke. These materials are stored in a steel silo with a capacity of approximately 30 m³, from where they are dosed into the process. As an alternative to the silo, "big bag" type sacks can also be used.

Dust, as well as sorption process products, is directed to the filter, where it is separated from the gas, and then transferred via a feeder system to hermetic steel containers. Negative pressure throughout the entire incineration installation, from the fluidized bed furnace, is maintained by a fan. Clean gases are discharged into the atmosphere via a chimney approximately 20 m high. The chimney has measurement ports installed for continuous monitoring of exhaust emissions. The sludge incineration process at the KALOGEO installation meets the requirements of EU Directive 2000/76.

The installation control system is fully automatic. Control in the PLC system (SPS) is conducted from a central control panel located in a closed room designated for the incineration plant operator, performing supervision duties within the incineration plant area. The operator has a direct view of monitors that record and visualize process parameters, such as combustion process temperature, energy consumption, status, and alarms.

The entire incineration installation is housed in a hall with dimensions of 20 m wide by 30 m long by 18 m high. A lime silo and ash containers are situated outside the hall.

Summary

The KALOGEO installation enables the incineration (utilization) of municipal sewage sludge pre-dried to approx. 45% dry matter (from 20% DM content). The system consists of drying and thermal processing in a stationary fluidized-bed furnace, where heat is partially used for sludge drying and excess heat can be sold. It is also possible to incinerate screenings and other organic waste.

  • Average capacity: 1.4 t/h

  • Total maximum capacity: 2 t/h (KALOGEO offers systems in the 10 t/h class)

  • Staff: 1 supervisor (fully automated system)

  • Process: Incineration at min. 850°C with low NOx emissions

  • Environmental impact: Odorless, practically no visible dust emission.

KALOGEO has developed a chimney-less incineration plant system that uses a scrubbing column instead of a chimney, with the result that effluent is transferred for re-treatment at the wastewater treatment plant. The technology offered by KALOGEO is a proven solution that has gained recognition in Austria and is successfully being implemented in other European countries, including China.

Forum Eksploatatora 05/2010 Author: Dr. inż. Roman Sobczyk

Abstract The article presents the KALOGEO fluidized bed sludge incineration plant. The method of operation of the installation and its individual components has been discussed. The fluidized bed incineration plant is a proven installation with all safeguards and process monitoring, and the applied KALOGEO technology provides a 100% guarantee that it does not emit pollutants into the environment that could have a negative impact.

Keywords: thermal sludge conversion, fluidized bed incinerator, KALOGEO, sludge incineration, biomass legal definition, sewage sludge disposal, EKOTOP, waste-to-energy, dry sorption.