Improving energy efficiency in waste water treatment: What emerging countries can learn from experience gained in the developed world

Transcription

1 Improving energy efficiency in waste water treatment: What emerging countries can learn from experience gained in the developed world Water Week 2009 Dr. Mark Husmann, Pöyry Environment GmbH, Germany 1

2 Development of energy prices and demand End user petroleum product prices & average crude oil import costs Worldwide primary energy demand by region (scenario) Mega Tons of Oil Equivalent Source: International Energy Agency, 2006 Source: 2

3 The Significance of Energy in Waste Water Treatment Distribution of Full Costs Germany Discharge fee 4% Sludge disposal 25 4% Percentage of Opex Personnel % Energy 14% Others 12% Depreciation 27% Interest 24% Distribution of Full Costs China Maintenance 6% Disposal 10% Chemical 12% Personnel 3% Energy 16% Cost of Capital 53% 5 0 percentage of energy costs is comparable Maintenance Disposal Chemical Personnel Energy 3

4 Energy consumption of wastewater treatment plants in Germany Electricity consumption of all WWTP in Germany ca. 4.4 TWh/a 35 kwh/(pe design a) or 0.4 kwh/m³ 0.7 % of the total electricity consumption in Germany 3 Mio. t CO 2 equivalents WWTP are the biggest single energy consumers of municipalities with a share of 20% of the total energy consumption. (source: German Federal Environmental Agency, 2008) In developing and middle developed countries the share can be expected considerably higher 4

5 Projects we have worked on recently Amount Country P.E. Influent Basic or detailed analysis Possible reduction of energy demand [m³/s] [%] 2 WWTP Brazil 9,000, basic 25 (Ø) 1 WWTP China 650,000 0,9 basic 40 1 WWTP Colombia 2,750, detailed 20 *) 1 WWTP France 200, detailed Ongoing 42 WWTP Germany 4,460, detailed 44 (Ø) 5 WWTP Tunisia 1,140, basic 76 **) (Ø) 52 WWTP 18,200, (Ø) *) Executed during the design phase **) Achieved by conversion of the process from aerobic to anaerobic sludge stabilization with energy recovery 5

6 What are the targets? Main targets Reduction of energy consumption Increase of energy production (self supply) Side targets Improvement of effluent quality Improvement of process stability 6

7 Criteria for further decisions on a general basis Energy evidence (example) Status Quo Target value Ideal value Δ target value Total specific energy consumption per p.e. 51 kwh/p.e. a 36 kwh/p.e. a 28 kwh/p.e. a Specific energy consumption aerated basin per p.e. 33 kwh/p.e. a 23 kwh/p.e. a 18 kwh/p.e. a Degree of gas reuse 56 % 98 % 99 % Degree of gas conversion to power / electricity 0 % 30 % 31 % Specific gas production per kg oss intake 370 l/kg oss 450 l/kg oss 475 l/kg oss Degree of independent supply Heat 97 % 97 % 98 % Electricity 0 % 49 % 65 % 15 kwh/p.e. a 10 kwh/p.e. a + 42 % + 30 % + 80 l/kg oss 0 % + 49 % Target values: Determined in several surveys of representative WWTP Ideal values: Developed at a model of an ideal WWTP (technical and electro technical equipment of best available technology, high efficient process technology, ) 7

8 General results Measures: Reduction of energy consumption Improvement of efficiency of individual units/aggregates Adjustment of the process Optimization of operating methods Adapted measurement and control technology Improvement of the degree of self supply in energy specific el. consumption [kwh/(pe*a)] Average results of all executed studies < > nominal capacity [PE] as is state WWTP reference value ideal value Degree of self supply [%] Average results of all executed studies < > Nominal capacity [PE] electricity as is electricity opt. Heat as is Heat opt. 8

9 Recommended Measures Reduction of hydraulic losses ca. 2 m efficiency: 40 % 4,5 Wh/(m³*m) at 3 m³/s saving potential: 340 MWh/a approx. 40 TUSD/a 9

10 Recommended measures Change from aerobic to anaerobic sludge stabilization 1 kg oss to be degraded 10 Aerobic Anaerobic consumption Ca. 2.3 kg O2 generation 0.8 m 3 Biogas 1.2 kwh Electricity Ca. 5.2 kwh Energy Use of Combined Heat and Power Unit (CHPU) 1.5 kwh Electr. (30%) 3.1 kwh Heat (59%) Option A Option B Option C Option D Process Biological BOD, N Biological BOD, N Biological BOD, N Biological BOD, N and P removal and P removal and P removal and P removal Primary Settling yes yes no no Sludge stabilization no yes, anaerobic no yes, aerobic Total investment costs 15 Mio USD 19 Mio USD 17 Mio USD 18 Mio USD Effective yearly costs Cost of Capital 1,4 Mio USD/a 1,7 Mio USD/a 1,5 Mio USD/a 1,6 Mio USD/a Energy costs 0,8 Mio USD/a 0,5 Mio USD/a 0,8 Mio USD/a 1,3 Mio USD/a Personnel costs 0,1 Mio USD/a 0,1 Mio USD/a 0,1 Mio USD/a 0,1 Mio USD/a Chemical costs 0,4 Mio USD/a 0,4 Mio USD/a 0,5 Mio USD/a 0,3 Mio USD/a Disposal costs 0,5 Mio USD/a 0,3 Mio USD/a 0,5 Mio USD/a 0,4 Mio USD/a Maintenance costs 0,2 Mio USD/a 0,2 Mio USD/a 0,2 Mio USD/a 0,2 Mio USD/a Total yearly costs 3,4 Mio USD/a 3,2 Mio USD/a 3,5 Mio USD/a 3,8 Mio USD/a Ratio 100% 94% 103% 112%

11 Recommended measures Optimization of Aeration Reduction of necessary aeration energy Exchange of destroyed aerators WWTP with 115,000 PE (design 190,000 PE), change to intermittent aeration of the aerobic basin Demand to date: aerators: recirculation pumps: TOTAL: 1,854,000 kwh/a 164,948 kwh/a 2,018,948 kwh/a 175,850 USD/a Demand optimized: Saving potential: % 302,842 kwh/a 26,380 USD/a Required Investment: Analyzers, installation: 45,500 USD 11

12 Lessons learned Problem: Acquisition of these type of projects in developing or middle developed countries is quite tough, as: In many projects the focus is just on investment costs and not on total yearly costs (incl. operational costs) Once the plant is in operation, there is no more money available for further optimization. Even a possible optimization is obvious, clients are hesitating to invest further money Solution: Germany launched an energy efficiency program, where studies have been funded by the Government (70% of the consulting costs). As a result more than 80% of potential beneficiaries executed these studies. Something similar was financed by KfW for first studies in Tunisia Precondition: Studies must be executed by external, not previously involved and experienced consultants 12

13 Lessons learned Costs: Costs for the studies without traveling costs and accommodation: Basic analysis: 5 TUSD 10 TUSD just first hints (not recommended) Detailed analysis: depending on size and technology Further investments: Costs [USD] All suggestions for optimization need a cost/benefit (C/B) calculation, considering the savings in operation costs and the investment costs including amortization Only measures with a cost/benefit ratio < 1 shall be carried out Immediate measures C/B << 1 with low investments < 20 TUSD Intermediate measures C/B < 1 with investments of approx TUSD Long term measures C/B 1 with investments > 150 TUSD Size of WWTP [PE] 13

14 Thank you for your attention 14