Metrics (and Methodologies) for Evaluating Water Saving Alternatives in a Typical Chemical Plant

Transcription

1 Metrics (and Methodologies) for Evaluating Water Saving Alternatives in a Typical Chemical Plant Presentation to the: June 19, 2013 Tom Carter, P.E. Sr. Program Manager, Heat Rejection Technology Johnson Controls, Building Efficiency thomas.p.carter@jci.com 1

2 Johnson Controls is a globally diversified company in the building and automotive industries Building Efficiency Power Solutions Automotive Experience 170,000 Employees Serving Customers in 150+ Countries $42B in Revenue in 2012 Headquartered in Milwaukee, WI 2

3 Evaporative Heat Rejection - The Primary Driver of Water Consumption in Many Processes Advantages Produces much cooler water temperatures than dry cooling which will: Disadvantages Consumes massive amounts of water and produces waste water improve process efficiency improve process capacity Lower in first cost than dry cooling Requires less parasitic energy than dry cooling Requires less plan area than dry cooling Requires chemical water treatment to combat issues related to corrosion, scale, and biological growth Creates potential for plume in cooler weather Potential for icing issues in freezing weather The Challenge: 1. How can the efficiency and capacity advantages of Evaporative Heat Rejection be delivered with far less water consumption? 2. How can you financially evaluate the alternatives? 3

4 Economic Overview When evaluating the total economic impact of water saving cooling alternatives to base cooling tower systems, a number of considerations must be taken into account: Economic Factors Favoring Water Saving Technologies: 1. Avoided cost of purchased water 2. Avoided cost of chemical treatment 3. Avoided cost of blowdown disposal 4. Ability to maintain full production during periods of water constraint Economic Factors Hampering Water Saving Technologies: 1. Additional capital cost for equipment 2. Additional energy cost 3. Additional costs related to lost production capacity (if applicable) 4. Need for additional real estate for the equipment Additional Factors To Consider: 1. Ease of retrofit into existing facilities 2. Impact on overall system reliability and maintainability 3. Public image relating to conserving water 4

5 Method #1 (The Simple One) Applicable for Cases in which: A. Water supply is not currently constrained nor is expected to be constrained in the future B. No change in water temperature being delivered to the process C. Objective is to save or replace water currently being consumed for economic or environmental reasons Methodology: 1. Calculate the Annual Cost of Water Saved (or Produced) ($/1000 Gallons) Annual Cost of Water Saved or Produced ($/1000 Gal) = Annual Cost of Energy, Materials, and Labor required for Water Saving Process ($) + Annual Capitalized Cost of Water Saving Equipment ($) Thousands of Gallons of Water Saved (1000 Gal) Note: Both the energy required and the amount of water saved are impacted by ambient weather conditions Therefore: An accurate performance model of the new process is required 2. Calculate Impact on Annual Plant Profitability Burdened Cost of Annual Cost of Water Water Saved or Produced = ( - ) x ($) ($1000 Gal) ($/1000 Gal) Annual Change in Profitability Thousands of Gallons of Water Saved (1000 Gal) 3. Calculate the IRR for the Investment 5

6 Method #2 (More Complex) Applicable for Cases in which: A. Current water supply is constrained or is likely to be constrained in the future Inputs needed for evaluation Assumed degree of constraint (% of annual water consumption) to be encountered Assumed constraint profile (magnitude, and duration) to be encountered Plant profitability model to evaluate overall profitability as a function of degree of constraint. B. Changes to the temperature of the water supplied to the process need to be evaluated Inputs needed for evaluation Cooling tower system performance as a function of ambient conditions Alternative system performance as a function of ambient conditions Process performance as a function of supplied cooling water temperature Temperature control strategies being used for both the current and alternative systems C. Primary objective is to mitigate risk of impaired plant profitability due to water constraints. Secondary objective may be to save water from an existing or new evaporative cooling process for economic or environmental reasons Methodology: 1. Calculate the Impact on Annual Plant Profitability of the Base and Alternative Technologies Under Various Degrees of Annual Water Constraint 2. Calculate the IRR for the Investment Under Various Degrees of Annual Water Constraint 6

7 Valid Evaluations Require Accurate System Models 1. Annual weather data (8760 hour TMY data), Not just Design Point Analysis 2. Production Requirements 3. Costs and constraints on the process inputs Energy Water Raw materials 4. Accurate model of the heat rejection systems being compared Design basis for the heat rejection equipment Energy inputs (fans and pumps) Cooling tower make-up requirements Capital costs of the heat rejections system components 5. Accurate model of the production processes Production efficiency as a function of the cold water temperatures Temperature control strategy for the cold water temperatures Capital costs of the balance of plant required for the product production 6. Understanding of the temperature control strategies impact on the process 7

8 Heat Rejection System Performance Varies Throughout The Year Therefore Performance Must Be Modeled At All Conditions Design Point 8

9 Heat Rejection Equipment Water and Energy Use Varies Throughout The Year functions of (Thermal Load, Control Strategy, WB / DB Temperatures) 9

10 Contour Plot of the Cooling Tower Make-up Water Requirements 10

11 Simplified Plant Schematic Material Energy Labor Capital Additional Inputs Alternative Technology Fan Energy Product Process CT Chemicals Make-up Water Pump Energy Blowdown 11

12 Simplified Business Unit Model Material Energy Labor Capital $ $ $ $ $ Additional Inputs Alternative Technology $ Fan Energy Revenue $ Product Process CT Chemicals Make-up Water $ $ $ Net Profit Business Unit $ Pump Energy $ Blowdown 12

13 Simplified Business Unit Model Inputs Location Material Energy Labor Revenue $/Unit Production Requirements Units/Hr $/Unit $/Unit Process $/Unit $/Year Capital Max HWT $/Year BTU s / Unit Min CWT Additional Inputs $/Year Alternative Technology CT Design HW / CW / WB CT $/kwh Fan & Pump Energy Chemicals $/gal of Blowdown Make-up Water $/gal CWT Impact on: Production Capacity Waste Heat Generated Unit Material Unit Energy Business Unit $/gal Blowdown 13

14 Process Inputs (Continued) Schedules Available for Electricity Prices, Production Requirements, and Water Availability 14

15 System Control Strategies 1. Heat rejection control strategies can impact both process efficiency and water use 2. Constant temperature heat sink (Production inputs are constant) Heat rejection equipment energy input varies with temperatures 3. Drive heat sink temperatures down as the ambient temperatures permit Production inputs vary as a function of the heat sink temperatures Heat rejection equipment energy input varies with production efficiency, control strategy, and temperatures 4. Optimized strategies that limit the dry heat rejection fan energy based on the Water to Energy Cost Equivalence Ratio (WECER) WECER = Cost of Water / Cost of Electricity WECER = $/1000 gal Water / $/kwh = kwh / 1000 gal 5. Adjust process temperatures to maximize production while minimizing water use in the face of water constraints 15

16 Process Schematic Output Detail Displays the key system parameters for each hourly condition 16

17 Process Schematic Output Example Adds key performance metrics and annual summary data 17

18 Business Unit Model Output Detail Displays the key cash flows for each hourly condition 18

19 Business Unit Model Output Example Adds key financial metrics and annual summary data 19

20 Examples of Impact of Water Constraint on Plant Profitability 20

21 Examples of Impact of Water Constraint on Investment IRR 21

22 General Conclusions: 1. Water constraints will have a significant impact on the ability to meet planned production requirements, profitability, and investment returns. 2. Alternative systems need to be evaluated at all anticipated conditions throughout the year, not just at the design points. 3. Robust system and economic models are required to fully understand the various performance and economic trade-offs. 22