Activated Sludge for Energy Recovery

Transcription

1 1st MALAYSIA NATIONAL SEWERAGE CONFERENCE Construction of Pantai 2 Sewage Treatment Plant Federal Territory of Kuala Lumpur Activated Sludge for Energy Recovery Jeffrey Too Heng Yuen, Low Thong Soon, Eng Wei Xiang By BEWG (M) SDN BHD 19 June 2013 Page 1

2 Introduction What does a Sewage Treatment Plant do? A STP treats raw sewage to meet effluent discharge standard, by consuming Energy and producing Waste Sludge Energy Sewage Treatment Plant Raw Sewage Clean Effluent Waste Sludge

3 Introduction Waste Sludge Energy Waste Activated Sludge (WAS) Sludge Dewatering Thickening Sludge Off Site Digestion Disposal Sludge Dewatering Off Site Disposal

4 Introduction Energy Depletion of fossil fuels Long Term Operational Cost Instead of Energy is consumed, Waste Sludge is generated Energy Waste Sludge A solution to turn part of the Waste Sludge into Energy should be adopted

5 Introduction Waste Sludge Energy Waste Activated Sludge (WAS) Sludge Thickening Sludge Digestion Biogas Sludge Dewatering Off Site Disposal

6 The Upgraded Pantai 2 STP At 2015

7 Process Flow Diagram Waste Activated Sludge Sludge Thickener Sludge Holding Tank Anaerobic Digester Sludge Holding Tank Centrifuge Decanter Sludge silo Biogas Heat Exchanger Boiler Transporter Condensate Trap & Stone Filter Biogas Flare Desulphurisation Biogas Holder CHP Biogas Engine Equipment

8 Sludge Related Processes

9 Waste Activated Sludge (WAS) Waste Activated Sludge (WAS) is the excess sludge to be removed from the biological reactor to maintain the balance of the microorganism for the biological treatment process. Very low solid content, <1% Unstable Page 9

10 Sludge Thickening Process Thickening is a process used to increase the solids content of sludge by removing a portion of the liquid fraction. It is generally accomplished by physical means of various type for thickening process. The sludge is designed to be thickened to 5%. Sludge volume 5 times less Less volume for pumping Page 10

11 Sludge Anaerobic Digestion Anaerobic digestion is a series of processes in which microorganisms break down biodegradable material in the absence of oxygen and produce biogas in anaerobic condition. Mesophilic digestion - optimally around 35 to 40 C Slow reaction, long HRT, huge tank Sludge is being mixed and recycled within the digester Energy is required to maintain the digester temperature Page 11

12 Sludge Anaerobic Digestion Through anaerobic digestion, the following could be achieved: Sludge is stabilized as biodegradable fraction is less Concentration of pathogen is reduced Biogas is generated as a by-product of anaerobic digestion process. Biogas contents 40-60% CH 4. It is a source of Renew Energy. Page 12

13 Sludge Dewatering and Disposal The dewatering process helps to reduce the water content within the sludge for better sludge handling before disposed from the plant. The solid content of digested sludge around 5% Required to be dewatered to 20% Storage facility is provided before off site disposal

14 Biogas Related Processes

15 Biogas Holder To provide storage for the biogas To maintain biogas pressure as biogas generation is not always stable Unstable supply of biogas will effect the downstream process/equipment

16 Biogas Treatment Biogas contents not only CH 4, it also CO 2, H 2 S, CO, H 2 O, N 2, etc. H 2 S and H 2 O is not favored in the downstream process. Biogas from digester is water saturated. It will form condensed water in pipe as the temperature drop. The H 2 S will damage downstream pipes and equipment even in low concentration Therefore, condensate trap, gravel filters, desulphurization tower is provided.

17 Biogas Engine The biogas generated from the anaerobic digestion will be collected and send for the biogas engine with combined heat and power system (CHP). Convert to electricity and supply for plant s internal consumption. Recover heat for sludge reheating to maintain the temperature within the mesophilic digester. Page 17

18 Cogeneration System

19 Heat Exchangers To recover heat and utilize for digester reheating Heat Exchanger 1 Biogas Engine - Water Heat Exchanger 2 Water - Sludge Page 19

20 Solid Line Area

21 Solid Line Layout Biogas Holder Sludge Silo Biogas Flare Sludge Holding Tank Biogas Pre-treatment Anaerobic Digester Biogas Biogas Boiler Room Generator Room Sludge Thickening and Dewatering Room

22 Normal Operation Set Up Biogas Anaerobic Digester Heat Exchangers Biogas Engine Electricity Page 22

23 During Starting Up Biogas Anaerobic Digester Heat Exchangers Biogas Engine Biogas generated is not sufficient to heat up the digester and maintain the process requirement Page 23

24 During Starting Up & Biogas Engine Maintenance Biogas Anaerobic Digester Heat Exchangers Biogas Engine Boiler Electricity A biogas boiler is used instead to ensure the heat required for anaerobic digestion. Page 24

25 Energy Saving for Pantai 2 STP When there is no energy recovery practice, additional heating is required in order to maintain the temperature of anaerobic digester For Pantai 2 STP, the heat required is covered by heat recovery from biogas engine. Energy Recovered for Re-heating Digester = 677kWh (Considered all losses) Additional Energy Provision = 330kWh x 2 of electricity

26 Energy Saving Comparison Scenario 1 No energy recover Anaerobic Digester Sludge Holding Tank Centrifuge Decanter Sludge silo Biogas Transporter Biogas Flare

27 Energy Saving Comparison Scenario 2 With energy recover Anaerobic Digester Biogas Condensate Traps and Stone Filter Sludge Holding Tank Heat Exchanger Centrifuge Decanter Boiler CHP Engine Sludge silo Biogas/Diesel Electricity Equipment Desulphurisation Biogas Holder Filter, dryer and Compressor Biogas Flare

28 Energy Saving for Pantai 2 STP Scenario 1 Biogas Flare Only Scenario 2 CHP Biogas Generator Time Hour Day Month Year Heat Recovered (MWh) Electricity Production (MWh) , , 782 Total (MWh) ,712

29 Energy Saving for Pantai 2 STP With heat recovery, can save Diesel consumption up to 49m 3 per month, 595 m 3 per year RM 114K per month, RM 1.39 million per year (Base on unsubsidized diesel price; diesel heat value; no losses consider) With electric generation, can save up to electricity 475 MWh per month, 5782 MWh per year RM 88k per month, RM 1.08 million per year (Base on TNB Industrial off-peak tariff rate) A total of more than RM 2.4 million cost saving per year!

30 Conclusion Solution to turn Waste Sludge into resources is very crucial. Turning it into Energy would be a good way. By introducing CHP Biogas Engine system, the biogas generated from anaerobic digestion would be sufficient to heat up the digester and generate electricity for STP internal use With the CHP system, the annual saving on energy for Pantai 2 STP is more than RM 2.4 millions.

31 Reference Metcalf & Eddy, Inc. Wastewater Engineering Treatment and Reuse ( Fourth Edition), McGraw Hill Companies, Inc, Pantai 2 STP Drawings, BEWG (M) Sdn. Bhd. Pantai 2 STP Solid Line Design Calculation, PURAC Environmental System (Beijing) Co., Ltd. TNB Tariff Price, Malaysia Diesel Price

32 BEWG (M) SDN BHD A wholly-owned Subsidiary of Beijing Enterprises Water Group Limited Page 32