Economical aspects of using cogeneration in wastewater treatment plants

Cost-effectiveness of cogeneration investments depends on the individual conditions in a treatment plant and should be carefully analysed. Analysis should be preceded by an energy audit. However, some characteristics remain unchanged in all installations:

  • The possibility of usage in urban areas due to high efficiency, modular design, and low gas and dust emission
  • Constant access to ‘free’ biogas from the IFC (Isolated Fermentation Chambers) installations
  • Heat production for the needs of the treatment plant – building heating, IFC process heating, sludge drying
  • Reduction of energy purchase rates from external sources
  • In case of voltage decay in external electricity grid, the possibility to power the plant by using synchronized generators in cogeneration modules
  • Lower transmission-caused energy losses
  • Rapid cost recovery after the cogeneration investment

The profitability of cogeneration investments depends on specific conditions of a treatment plant and should be subject to analysis preceded by an energy audit. It is assumed that the minimum size of a cogenerator is 100 kWh of electrical power (for a treatment plant of 60 000 PE)


An example of a CHP system operating in a wastewater treatment plant with a throughput of 26 400 m3 / day

Advantages of burning biogas in cogeneration systems

  • The usage of biogas created during sludge fermentation may significantly increase the profitability of public utility services
  • The usage of biogas as fuel limits CO2 emissions
  • Burning biogas in gas engines is considered to be an environmentally friendly technology
  • EU support for investments of this kind
  • Reduction of the emission of environmentally harmful substances
  • Reduction of the amount of energy taken from external electricity grid
  • Reduction of greenhouse gases emission by eliminating the usage of torches (torches are used only in emergency states of the system)

Technical aspects of using cogeneration in wastewater treatment plants

CHP unit power range

Depending on the type of engine used we offer the following power ranges in cogeneration units:

  • MAN (30-530 kW)
  • MWM (400-4300 kW)
  • Perkins (300-1000 kW)
  • Liebherr (140-500 kW)

Casing types

We offer several types of casing:

  • Frame – without any silencing systems
  • Soundproof casing, used mostly for indoor installations
  • External soundproof containers

Operating mode

  • Working parallel to the network
  • Working parallel to the network, with the possibility of reserve work
  • Synchronization of multiple cogeneration units

Regulation of CHP units

  • By heat reception
  • By consumed electricity
  • By the amount of biogas

Additional equipment for CHP installations

Biogas preparation stations:

  • Active carbon filters
  • Chemical and microbiological desulphurization
  • Biogas blowers and press knots
  • Biogas drying stations (cooling and heating)
  • Biogas torches
  • Biogas analysers

Measuring systems conforming to the demands of The Energy Regulatory Office:

  • Gross electricity meters
  • Heat meters
  • Gas meters

Problems caused by incorrect biogas preparation

Exploitation issues:

  • System corrosions leading to malfunctions
  • Lower income
  • Premature definite consumption
  • Efficiency reduction

Increase in exploitation costs:

  • More frequent reviews
  • More frequent oil changes
  • Shorter periods between general renovations

Biogas desulphurisation

Microbiological:

  • H2S concentration<10 000 ppm
  • Maximum biogas flow: 3 500 m3/h

Dry with constant deposit:

  • H2S concentration<15 000 ppm
  • Maximum biogas flow: 1 5000 m3/h

Removing siloxans from active carbon filters:

  • Combined with a drying station

Examples of our work

CHP system construction for the ‘Żydomice’ wastewater treatment plant

The task consisted of complete construction and executive projects, based on the installation of a CHP unit powered by biogas, with heat output of 225 kW and electrical power of 190 kW.

 

The task included the following:

  • technological design
  • construction design
  • obtaining the environmental decision
  • obtaining the construction permit
  • industrial executive projects
  • technical specification of the execution and collection of works
  • works pre-measurements and investment cost estimation
  • expertise and inventories
  • geological surveys
  • acoustic protection project

Modernisation of the ‘Południe” wastewater treatment plant regarding sludge management in order to increase energy efficiency within the ‘design and build’ system

The task was a multi-sector project, based on the installation of two CHP units powered with biogas, with heat output of 910 kW and electrical power of 730 kW.

 

The scope of the project included:

  • Preparation of material and financial schedules
  • Preliminary project
  • Construction project
  • Executive project
  • Installation works
  • Construction works
  • Desulfurization system

 


Construction of a complete energy system based on the installation of a CHP aggregate with a CFC (Closed Fermentation Chamber) system in the Water Supply and Sewage Systems Plant ‘Sława Ltd’

The subject of the contract was the preparation of project documentation for the task ‘The construction of a complete energy system based on the installation of a CHP aggregate with a CFC system in the Water Supply and Sewage Systems Plant ‘Sława Ltd’.’ The heat output of the used system was 127 kW and the electrical power was 104 kW.

 

The task included the following:

  • construction project along with construction permits
  • executive project
  • works pre-measurement and investment cost estimation
  • technical specification of the execution and collection of works

 

 


Ecokube sp. z o.o.

ul. Wólczańska 128/134

90-527 Łódź

tel. + 48 42 630 66 00

biuro@ecokube.pl