Boiler and Steam Efficiency What does it mean?

Transcription

1 PACIA Carbon Solutions Forum 3-29 September 20 Boiler and Steam Efficiency What does it mean? Andrew Hook - Area Manager, Nalco 1

2 Purpose, Process, Payoff Purpose: To explain boiler and steam efficiencies through case studies, and impact on carbon Process: Initial definitions Walk through real-life examples, discussing impacts on carbon Payoff: Awareness of ways to impact on efficiency Routes to getting more information 2

3 Boiler Anatomy 3

4 Boiler efficiencies and Carbon? Steam is generated through combustion of fuel Fuel : C x H y +(X+[Y/4])*O 2 -> XCO 2 +Y/2*(H 2 O) Want to maximize the energy obtained from this combustion Hence, any losses from the boiler box and stack losses reduces efficiency Efficiencies of boilers (and steam systems) are a function of the losses: Overall Efficiency ( Heat loss method ) can be defined as: (T AFT T STACK )/(T AFT T AMBIENT ) *100 Where AFT=Adiabatic Flame Temperature Stack = Flue Gas Temperature Ambient = Ambient Dry Bulb 4

5 For the test later on 5

6 Boiler efficiencies and Carbon? This method of efficiencies is the input - output method: Net Energy contained in steam / (Total energy obtained from combustion) *100 Rules of thumb: CO 2 generation per tonne of fuel burnt (normal efficiencies) Natural Gas : 2.8 tco 2 /t fuel Oil : 3.0 tco 2 /t fuel Black Coal : 2.3 tco 2 /t fuel Note that NG has a higher energy content 6

7 What are normal efficiencies? Boiler Efficiency will never be 100% Losses: Insulation Stack Air is 79% Nitrogen, 21% Oxygen, so most air is along for the ride! Water generated in combustion carries latent heat out the stack too! Typical boiler efficiencies: Natural Gas: 80-85% Oil: 75-80% Black Coal: 75-78% 7

8 Case Study 1: Economizer Failure 8

9 Case Study 1: Economizer Failure Failure of economizers led to 40 C reduction in feedwater temperature What is the loss in efficiency? What is the CO 2 impact? Cost? Why did they fail? Loss of efficiency: Loss of each 6 C = 1% efficiency (roughly) Therefore, lost around 6% efficiency (from 80%) CO 2 impact and Cost: Prior to failure, used around 10,000 m3/day of natural gas, after 12,000m3, running around 7500 hr/yr, $3.41/GJ Extra 1750 t/year CO 2, $99,100/yr cost increase ($57/t..) Failure? Poor deaeration of feedwater Remedy on-line monitoring of feedwater and control of oxygen scavenger 9

10 Case Study 2: Tube Scaling 10

11 Case Study 2: Boiler Scaling Deposition of scale led to approx 2% increase in fuel and increase in stack temp of around 45 C What is the loss in efficiency? What is the CO 2 impact? Cost? Why did this happen? Loss of efficiency: Increase of each 22 C in stack temp = 1% efficiency (roughly) Therefore, lost around 2% efficiency (from 80%) CO 2 impact and Cost: Current: 473, 000 GJ/yr fuel, 8000 hr/yr at around 2% fuel increase, around 3.41 $/GJ as natural gas Extra 570 t/year CO 2, $32,250/yr cost increase Failure? Use of dirty precipitating phosphate program on poorly softener water Remedy monitor hardness breakthrough from boilers, use solubilizing chemical program, watch cycles 11

12 Case Study 3: Cycles of Concentration Boiler in Case Study 1 running at 20 cycles of concentration (expect 50 cycles) What is the loss in efficiency? What is the CO 2 impact? Cost? Why is this happening? Loss of efficiency: Approximately 1% CO 2 impact and Cost: Using around 10,000 m3/day of natural gas, running around 7500 hr/yr, $3.41/GJ, water around $1/kL Extra 993 t/year CO 2, $65,960/yr fuel cost increase, $14,100 water increase Why is this happening? Habit and focus on cycles Remedy monitor cycles, push to limits, but no more than 50 in low pressure boilers (HP ) Technologies available for tight control 12

13 Case Study 4: Cycles of Concentration Boiler in Case Study 1 running at 30% condensate return (expect 50%) What is the loss in efficiency? What is the CO 2 impact? Cost? Why is this happening? Loss of efficiency: Approximately ZERO (as boiler efficiency!) CO 2 impact and Cost: Using around 10,000 m3/day of natural gas, running around 7500 hr/yr, $3.41/GJ, water around $1/kL Extra t/year CO 2, $176463/yr fuel cost increase, $92211 water increase Why is this happening? Leaks habit, and focus on condensate return% Remedy monitor return and condensate % return and elevate priority 13

14 Reference Sites US Department of Energy (DOE) Great site, many, many worked examples EREP website: The internet is a great resource for many tips Nalco Water Handbook (plug for our company!) 14