Halle-Lochau in Saxony-Anhalt chosen as location in 2017

The plant for thermal sewage sludge utilisation is being built in the Halle-Lochau recycling and resource management park. This is located on the site of the Halle-Lochau landfill in the Döllnitz district of the municipality of Schkopau. The facility is located at the site with good transport links between Halle (Saale) and Leipzig and will cover a total area of approximately 5,000 m².

Due to its geographical proximity to the site, WTE Betriebsgesellschaft mbH (WTEB), a subsidiary of WTE Wassertechnik GmbH based in Hecklingen, will take over the technical management of the plant.

Recycling of more than 33,000 tons of sewage sludge per year using state-of-the-art technology: The technical plant concept

In the future, the sewage sludge mono-incineration plant will be operated around the clock – 24 hours a day, seven days a week. The incineration concept is designed in such a way that about 33,000 tons of dewatered sewage sludge as well as 2,750 tons of externally dried sludge can be processed per year.

The thermal utilisation plant consists of the following components:

• Fuel reception including bunker crane
• Drying including vapour treatment
• Combustion system and boiler
• Energy utilisation (back-pressure steam turbine)
• Flue gas cleaning
• Chimney with emission measurement
• Ash silos

The following buildings or structures will be erected for the placement and assembly of the various units of the sewage sludge mono-incineration plant:

• Sewage sludge transfer area: bunker building (with bunker exhaust air treatment)
• Dryer building (drying, vapour treatment)
• Plant building (fluidised bed furnace, boiler plant and flue gas cleaning)
• Social building with low-voltage room (including control room), emergency power, compressed air and turbine room

A decisive role in the operation of the plant plays its degree of automation: the operation of the thermal utilisation plant is planned as a 72-hour operation without permanent supervision (BosB mode). The comprehensive automation equipment ensures a high level of supply security for the entire plant. In addition, the plant can also be permanently monitored via secure remote access in accordance with the latest state of the art.

The main data and parameters of the plant:

Operator-friendly and efficient: Sewage sludge logistics

The dewatered municipal sewage sludge is delivered by truck and weighed by a weighbridge on site. The wet sludge is dumped into a receiving bunker, and a crane system then feeds the mixing bunker, where further mixing and homogenisation of the sewage sludge takes place. A crane then transports the sewage sludge to the receiver for drying and incineration. Before this, the sludge passes through an impurity separator. In addition to dewatered sewage sludge, fully dried sewage sludge with 90 % dry residue (DR) is also delivered externally and temporarily stored in a dry sludge silo.

Economical and flexible: Drying and fluidised bed incineration

A particular focus of the entire treatment plant is on nearly wastewater-free operation. Therefore, a belt dryer is used as drying unit. For this purpose, a HUBER Belt Dryer BT size 20 was installed, thus making use of the long-standing know-how of one of the two parent companies of S2E.

In addition, the full drying concept allows a significantly better utilisation of the dryer capacity of < 50 tonnes per day, which is limited due to the simplified approval procedure. The partial stream of sewage sludge dried to 90 % DR is remixed with the remaining dewatered sewage sludge to approx. 45 % DR before incineration, which ensures self-sufficient combustion in the stationary fluidised bed incinerator.

Highly efficient and low in pollutants: Stationary fluidised bed technology

Stationary fluidised bed technology has not only established itself as a promising and proven process for thermal sewage sludge utilisation, but is also a particularly efficient and low-pollutant technology for the incineration of sewage sludge. The sewage sludge to be disposed of is fed into an incineration line (consisting of a furnace and waste heat boiler) with downstream flue gas cleaning.

The mixture of sand, ash and sewage sludge is fluidised by the injection of preheated primary air from below through the nozzle floor. The sand is thus transformed into a fluid-like state. The open design of the nozzle floor allows foreign matter to be discharged and the sand to be recirculated during operation – without shutting down the firing system and impairing operation.

Flexible control of the firing rate and minimisation of pollutant emissions

The flexible firing rate control ensures that the sewage sludge is completely burnt by staged air control. In order to minimise pollutant emissions, it is possible to react flexibly to fluctuations in load and calorific value. Already in the combustion chamber, it is also ensured that pollutants, e.g. dioxins, carbon monoxide (CO), organic pollutants and nitrogen oxides (NOx), are minimised. An ammonia water injection system can also be retrofitted in the combustion chamber (SNCR process) if required.

The firing system is designed in such a way that the sewage sludge with 45 % DR can be burnt without additional fuels. An oil burner is used to compensate for unsteady operating conditions (e.g. in the event of fuel failure or if the temperature falls below the specified combustion chamber temperature) and to start up and shut down the plant. The burner system is operated automatically via the central control system.

The flue gases are cooled in the waste heat boiler, which is connected to the secondary combustion chamber. In the waste heat boiler, the energy from the flue gas is transferred to a water-steam system and the resulting steam is converted into electricity by a steam turbine.

Energy utilisation and generation: Half of the demand for own electrical energy covered

The hot flue gas is fed to the waste heat boiler and cooled in the steam production system for subsequent flue gas cleaning. The thermal energy released during the incineration of the sewage sludge is transferred to the water-steam system in the saturated steam boiler. A steam turbine and a downstream generator utilise the energy of the steam produced. To ensure the highest possible plant availability, the turbine for energy utilisation is designed as a back-pressure steam turbine.

The exhaust steam from this turbine is in turn largely used for drying the dewatered sewage sludge. Excess heat is released into the ambient air via a cooler. The optimised energy concept can cover half of the entire plant’s own electrical energy requirements.

Environmentally friendly and state-of-the-art: Flue gas cleaning

In order to minimise emissions of harmful gases during flue gas cleaning, S2E chose state-of-the-art technology. A dry flue gas cleaning system is used for the Halle-Lochau mono-incineration plant. This variant does not produce any wastewater from flue gas cleaning, which is an innovative and sustainable advantage.

The flue gas purification system consists of:

• Fabric filter for pre-separation of the fly ash
• Dry additive dosing: addition of activated coke and hydrated lime to the flue gas stream (sorption reactor).
• Particle recirculation and conditioning
• Fabric filter (sorption filter)
• Ash removal and bufferingg

The quasi-dry, conditioned sorption stage with the dosing of hydrated lime and activated coke in a reactor forms the second stage. The powdered sorbents are separated and removed in the second fabric filter together with the pollutants bound to them, whereby the separated particles are partially recirculated. This results in more efficient separation of the pollutant components while at the same time reducing the need for sorbents.

The cleaned flue gas is conveyed via the induced draught fan into the stack, where the pollutant gas and particle concentrations are continuously measured, which are then evaluated and recorded in the emission measuring station. The dusty ashes are stored separately in silos and can then be transported away.

With the selected flue gas cleaning process, the pollutant gases, dust, heavy metals and polychlorinated dibenzodioxins and dibenzofurans (PCDD/F) can be separated in a very economical way. This design of flue gas cleaning ensures compliance with the required emission limits according to the 17th Ordinance on the Implementation of the Federal Immission Control Act (BImSchV).

Phosphorus recovery: Ashes as valuable raw material

Sewage sludge mono-incineration achieves the highest rates of phosphorus recovery with simultaneous destruction of all pollutants – with subsequent phosphorus recycling from the ash produced. The sewage sludge ash from fluidised bed incineration is very low in pollutants and represents a significant phosphorus carrier. Thus, it will be a valuable feedstock for the future production of fertiliser from phosphorus.

High-quality recycling of phosphorus-containing ash is the future

It can already be observed that, with regard to the mandatory recovery of phosphorus after the expiry of the transitional periods from 2029 or 2032, the mono-incineration of sewage sludge, together with the high-quality recycling of the phosphorus-containing ashes produced, is being intensively pursued in Germany as a matter of priority.

In order to keep an eye on the future obligation to recover phosphorus already today, sludge2energy GmbH is looking at sustainable and efficient recycling routes for the phosphorus-containing ashes.

Cold commissioning since mid-July 2021, hot commissioning at the end of September: The milestones of the project

• November 2018: Application for construction of the plant
• November 2019: Start of construction
• 15 and 16 January 2021: Installation of the fluidised bed furnace
• 31 March 2021: Boiler pressure test passed
• June 2021: Completion of assembly of all plant components and testing of all pressurised component groups
• Since mid-July 2021: Cold commissioning
• Mid-October 2021: First sludge fed, followed by performance tests and trial operation
• Start of regular operation and handover to WTE Betriebsgesellschaft mbH scheduled for 01 March 2022.

Learn more about the this project and the sustainable sludge2energy process at www.sludge2energy.de.