Options to reduce cooling water consumption in industrial plants

Transcription

1 Options to reduce cooling water consumption in industrial plants Discussion of challenges, tools and case studies Edgar Amaro-Ronces, Andrew Sloley, Eberhard Lucke CH2M Texas Industries of the Future - Water Forum November 5, 2015

2 Options to reduce cooling water consumption in industrial plants Introduction Challenge Methodologies Tools Case Studies Conclusion 2

3 Introduction Key theme for many projects: water sustainability Maintain Support Endure Cost of treatment for supply (water sources) and discharge (water sinks) Future trends in industry and facility design Adopt efficient systems that minimize use of fresh water Challenge exists across all major industries Water re-use and recycling Pitfalls Environmental regulations 3

4 Challenge How to deal with the complexity of the issues around water, e.g. cooling water demand? Broad range of applicable methods to model/describe the problem Each with specific strengths and weaknesses Factors like complexity of the heat exchanger network (HEN), capital cost, operating and maintenance cost, safety, required treatment Constraints like limited sources, limited discharge options, financial limitations, existing hardware systems, water versus air cooling Complexity of problem challenges the application of tools that allow finding the optimum solution to the problem 4

5 Methodologies Technical models Spreadsheets (e.g. water balance); Pinch Analysis; Process Simulation (static, dynamic) Financial models CAPEX models; OPEX models; Combined models; other cost factors Mathematical models Genetic Algorithm (GA); Ant Colony Optimization (ACO); Particle Swarm Optimization (PSO); Cat Swarm Optimization (CSO) Engineers Knowledge; Expertise; Judgement 5

6 Water Pinch Analysis 6

7 Water Pinch Analysis [1] Strengths Well known methodology with proven success record Several software options available on the market Has been further developed to expand range of application Weaknesses Provides a technical solution only Financial considerations need to be factored in via separate model Tends to create very complex networks that lack practical application Limited to application within the process itself Very difficult to apply to solving multi-component systems 7

8 Financial Models [2] Requires Constraints Required to solve the problem = minimize objective function Overall heat balance for each stream must be solved Minimum temperature approach limit must be met Non-negativity for Energy Streams must be maintained Mass conservation in branches must be met 8

9 Mathematical Models and Algorithms [3] Example: Cat Swarm Optimization Models the behavior of CATS to solve the optimization problem CSO Algorithm has two sub-models: Seeking mode: moves carefully and slowly Tracing mode: runs after target Strengths Powerful algorithm that finds better solutions than most other approaches Weaknesses Not a typical engineering tool Requires detailed mathematical knowledge Requires very high computation time 9

10 Example: VOYAGE TM 10

11 My Favorite Tool Process Engineer 11

12 Case Study: Vacuum Ejector Condensers Vacuum condenser cannot condense motive steam Suction load to 2 nd stage ejector too high Suction pressure of 2 nd stage ejector too high Vacuum tower pressure too high Final result gas oil left in vacuum residue Problem identified as cooling water supply rate 12

13 Cooling Water Survey 13

14 Solutions Possible Booster pump Used Looping of cooling water header Butterfly valve for system balancing Implications No new cooling water made More control over allocation between existing units 14

15 Case Study: HF Alkylation Reactor Temperature Reactor temperature reaches 110 F Reduced octane of alkylate Cooling water supply temperature in summer was 100 F Problem is cooling water supply temperature Wet bulb approach is F Ideal operation of reactor ~85 F 15

16 Reactor Temperature Survey 16

17 Solutions Upgraded cooling tower to get down to 88 F New fill +0.3 to +0.5 RON on alkylate Other steps possible Improve cooling-tower fans too expensive Booster pump for cooling water supply other units also constrained Shifting services to air-fins to make more cooling available plot plan constraints 17

18 Case Study: Ammonia/Fertilizer Plant [4] Summary Idea # 1 Reduce Cycle of Concentration: $280,000/year Idea # 2 Treat Wastewater and Re-Use: $150,000/year Idea #3 Steam Boiler Blowdown as Make-Up: $14,000/year Idea #4 Replace Drift Eliminators: no short term savings Total savings: $444,000/year Reduced make-up water by 228 m 3 /h (38% reduction) Required optimization of chemical treatment system to give desired flexibility for reduced COC and multiple make-up water streams 18

19 Conclusions Sustainable water sourcing will gain in significance Especially in remote areas with limited water sources Also in areas with competing water users We have a lot of tools available, we just have to understand their strengths and their limitations There is no universal approach for all the different challenges In most cases an integrated approach using multiple tools will be required The Process Engineer is the glue that keeps it all together Even small and simple studies can yield significant results 19

20 References 1. Pinch Analysis: For the Efficient Use of Energy, Water & Hydrogen, Natural Resources Canada, An Energy Integration Approach on UHDE Ammonia Process, Alnouss M. Ahmed, Al-Nuaimi A. Ibrahim, International Scholarly and Scientific Research & Innovation 6 (11), Optimization of Heat Exchanger Networks using an Evolutionary Method, Abolfazl Ghiasvand, Alireza Fazlali, Tayebeh S. Ghiasi, Mahdi Aliyari- Shoorehdeli, Amir H. Mohammadi, Advances in Energy Research Volume 18, Chapter 10, Optimization of Make Up Water Reuse Saves $100,000/yr for Ammonia Plant, Davor Kesner, Tanja Vulinec Losso, GE Water & Process Technologies,

21 THANK YOU! 21