Identifying and Quantifying Energy Savings on Fired Plant Using Low Cost Modelling Techniques

Transcription

1 Sustainable Thermal Energy Management Conference Identifying and Quantifying Energy Savings on Fired Plant Using Low Cost Modelling Techniques Bob Tucker (Zerontec Ltd) John Ward (University of Glamorgan) SusTEM 2010, Newcastle

2 Outline Brief description of the models Example applications Metal reheating Fired heater (petrochemicals)

3 How models can help? Energy savings Improved investment decisions Reduced risk Improve/maintain product quality Increased production Meet environmental commitments

4 Project benefits Objectives: Save Energy, Reduce cost, Reduce C Solution 1 Solution 2 Examples: Flue stack heat recovery Improved insulation Improved controls Oxy-enriched firing High emissivity coatings Modelling/ Simulation Solution n

5 The ZONE model - an example of a long furnace model Furnace divided into gas and surface zones Radiation transfer calculated between all zones Heat balance equations solved zone by zone Steady-state models Transient models

6 Transient ZONE model START READ INPUT DATA t = t + t ZONE MODEL calculate heat fluxes to wall and load TRANSIENT CONDUCTION ANALYSIS calculate new wall and load temperatures CHANGE PROCESS CONDITIONS e.g. fuel input rate END

7 Example output data

8 Single well-stirred steady-state zone model

9 Predicted savings on a small continuous metal reheating furnace Flue gas O 2 % Oxidant Air preheat T o C Exhaust T Base case 4.6 Air o C Fuel saving % Improved air/fuel ratio 1.1 Air control Flue stack recuperator Flue stack regenerator Oxy enriched firing 1.1 Air Air Oxy/gas firing

10 Simple fired heater model Steady-state single zone model Use of model to investigate effect of high emissivity wall coatings

11 High Emissivity Coatings High-ε coatings are commercially available Emisshield Enecoat Emi-coat Exaggerated energy saving claims Need more accurate spectral gas band models to predict savings Spectral effects can be easily included in the single well-stirred zone model

12 Refractory Wall Emissivity Effect Absorption and reradiation by wall Emission Increased transmission to load Absorbing gas bands Load flame Needs a realistic representation of the spectral properties of the gases

13 Predicted effect of wall coating on a fired heater Base case e=0.5 Wall coating (Emissivity = 0.93) Base case Constant thermal output Constant bridge-wall T Constant bridgewall T ; Enlarged convective section Fuel input MW net MW net Bridge-wall T o C Output MW (6.2% increase) 7.03 (11.9 % increase) Efficiency % net There is negligible fuel saving to be achieved in this case BUT Production throughput could be increased by up to 12%

14 Dynamic single zone model for a batch heating furnace L o a d te m p e r a tu r e o C U n c o a te d r e fr a c to r y R e fr a c to r y e m is s iv ity = tim e, m in u te s

15 ENERGY SAVINGS WITH MULTIPLE LOADS Max. high fire rate kwnet Total fuel use (8 cycles) GJnet/tonne Cycle time (charge 8) mins. Uncoated walls Coated, ε= (3.4%) 52.9 Coated, ε= (2.88%) 53.9

16 Small forge furnace Options: 1) Base case furnace as found 2) Replace refractory walls with lightweight ceramic fibre 3) Improved flue gas recuperator 4) Option 2 and 3 combined 5) Recuperative burner installed on base case

17 Dynamic long furnace model The Long Furnace Model Fuel inputs Flue Load Load Zone 1 Zone i T Gas Wall Load 11 volume zones; 35 surface zones (load, roof & walls) Time step = 5 secs. Thermal input modulation Temperature dependent properties

18 Results for small forge furnace CASE Condition Overall SFC* Fuel saving Throughput Billet T difference GJ net /Tonne % kg/hr o C 1 Base case Ceramic fibre walls and roof Flue stack recuperator Options Recuperative burner * Specific fuel consumption The recuperative burner option is likely to lead to reduction in productivity and product quality

19 Transient simulation of steel temperatures in a reheating furnace Soak zone Heating zone Preheat zone Recuperation zone Fuel saving % T o C Base case 7% 50% 43% - 56 End recuperator Regenerative burners 7% 50% 43% % 18% 25% 25% 25% Steel T o C Base case End recuperator Regenerative burners Zone no.

20 SUMMARY & CONCLUSIONS Low cost ZONE models provide powerful, accurate and fast solution of complex systems Single zone steady-state Single zone transient 1-D long furnace models (steady-state & transient) Provides fast evaluation of alternative investment decisions Can increase confidence and help remove barriers to investment in energy saving technology Minimal hardware resources required Memory and CPU speeds not an issue

21 Turning Ideas into Profit! Science/ Technology Difficult! Modelling can help Easy!

22 Thank you!