design & analysis of a biogas fuelled trigeneration system for … · 2012-05-08 · biogas...

Design & Analysis of a Biogas Fuelled

Trigeneration System for a Brewery

Student: Robert McKeon

Supervisors: Dr Yaodong Wang, Professor Tony Roskilly

Introduction

• Aims of the project:

– Undertake an energy audit of the brewery and its

processes

– Design & propose a trigeneration system

– Offer the designed system to Wylam Ltd.

Objectives

• The main objectives of the project were:

1. Understanding the brewing process

2. Undertaking the Energy Audit

3. Based on the results, design a suitable trigeneration

system

4. Offer the system to the company to help them achieve

their renewable aims

Design Cases

• There were 6 design cases investigated during the project:

1. Biogas trigeneration system

2. Biodiesel trigeneration system

3. Oil trigeneration system

4. Biogas CHP system

5. Biodiesel CHP system

6. Oil CHP system

Trigeneration & CHP

• Trigeneration uses one fuel source to provide three forms of output energy:

1. Heat

2. Cooling

3. Power

• Increases overall efficiency of the system

• Extracts more energy from the fuel source

• CHP produces Heat and Power from the fuel source

Energy Audit

• Undertaken to find

– Energy usage of the brewery

– Where areas of improvement were needed

– Capacities needed for system design

• Each process examined fully to find energy inputs and outputs

• Electrical components also included in audit

Floor Plan

Energy Audit Results

• The results from the energy audit gave the energy supply needed from the proposed system

• The system capacities were:

– 131 kW Heat

– 23.7 kW Cooling

– 20 kW Power

System Design

Eclipse

• Programme used to model the design cases

• Setup in three stages

1. Flow diagram

2. Mass & Energy balance

3. Utility

• Results show energy produced by the system

Eclipse

Base Case

• Base case design used to keep parameters the same to ensure good comparison of fuels

• Design using 28 sec oil used by brewery

• Fuel flow rate and some components/parameters changed to achieve full load

• Genset produced 120 kW to produce enough heat energy

• Absorption chiller base case was also used

• Not changed however due to its complexity

Fuels

• Biogas Composition:

• Biodiesel:

– Waste vegetable oil was used as a cheap, easily accessible option

• Fuel Oil:

– 28 sec oil used which is already imported onto site

Compound Percentage of biogas

CH4 50.97%

CO2 45.35%

N2 3.66%

O2 0.01%

Results

• Separated into the 3 fuels for analysis and comparison

• CHP and trigeneration systems compared including:

– System outputs & availability

– Efficiencies – overall & electrical

– Emissions

Biogas Results

• Could run both Copper and HLT at the same time

• Produced the most output energy

• Highest efficiency system as expected

Case 1 - Both running

Required Available Ratio (%)

Copper heat requirement 61.2 kW 64.7 kW 105.7

HLT heat requirement 69.8 kW 72.5 kW 103.9

Heat for absorption unit 50.1 kW 51.2 kW 102.2

Power output 120 kW 120.9 kW

Case 4 - Biogas CHP





Biogas Results

Biogas Results

EFFICIENCIES

Case 1 Both Case 4

Biogas Lower Heating value (MJ/kg) 25.54 25.54 MJ/kg

Biogas flowrate (kg/s) 0.01338 0.01338 kg/s

Primary energy consumed (kJ/s) 341.7 341.7 kJ/s

Power output 120.9 123.2 kW

Engine electrical efficiency 35.4 36.1 %

Heat for Copper 64.7 70.5 kW

Heat for HLT 72.5 79.3 kW

Heat for Absorption 51.2 -- kW

Total Heat from exhaust + cooling water 188.4 149.8 kW

System Efficiency 90.52 79.89 %

Heat to Power ratio 1.56 1.22

Biogas Results

System requires the most capital investment

However achieves the greatest savings

Efficiency of system increased by 43&55% for CHP and trigeneration respectively

Emits higher levels of N2 than the other systems

Outputs lower than expected for system

Fuel flow rate too low for maximum output

System could not cover all capacities

Biodiesel Results

Case 2 - Both running






Copper running



HLT heat requirement 69.8 kW 0 kW 0.0



HLT running


Copper heat requirement 61.2 kW 0 kW 0.0




Biodiesel Results

Case 5 - Biodiesel CHP

Heat from Fuel oil Required Available Ratio (%)




Biodiesel Results

Biodiesel Results EFFICIENCIES

Case 2 Both Case 2 Copper Case 2 HLT Case 5

Biodiesel Lower Heating value (MJ/kg) 39.66 39.66 39.66 39.66 MJ/kg

Biodiesel flowrate (kg/s) 0.00814 0.00814 0.00814 0.00814 kg/s

Primary energy consumed (kJ/s) 322.6 322.6 322.6 322.6 kJ/s

Power output 110.4 110.4 110.4 112.5 kW

Engine electrical efficiency 34.2 34.2 34.2 34.9 %

Heat for Copper 50.7 112.4 0.0 66.5 kW

Heat for HLT 61.4 0.0 110.1 75.9 kW

Heat for Absorption 51.1 51.8 51.9 -- kW

Total Heat from exhaust + cooling water 163.2 164.2 162.0 142.4 kW

System Efficiency 84.80 85.11 84.43 79.00 %

Heat to Power ratio 1.48 1.49 1.47 1.27

Efficiencies of system good considering low output

Indicates that with correct parameters could be a good system

Main issue is logistics of collecting and importing vegetable oil

Lower emissions than Biogas system

Biodiesel Results

Case 6 – Fuel Oil CHP





Fuel Oil Results

• Simplest and cheapest system to install

• Achieved higher output than biodiesel system

• Could not run Copper and HLT at the same time

Fuel Oil Results Case 3 - Both running






Copper running



HLT heat requirement 69.8 kW 0 kW 0.0



HLT running


Copper heat requirement 61.2 kW 0 kW 0.0




Case 6 – Fuel Oil CHP





Fuel Oil Results

Fuel Oil Results EFFICIENCIES

Case 3 Both Case 3 Copper Case 3 HLT Case 6

Fuel Oil Lower Heating value (MJ/kg) 42.893 42.893 42.893 42.893 MJ/kg

Fuel Oi flowrate (kg/s) 0.00814 0.00814 0.00814 0.00814 kg/s

Primary energy consumed (kJ/s) 349.0 349.0 349.0 349.0 kJ/s

Power output 120.1 120.1 120.1 122.3 kW

Engine electrical efficiency 34.4 34.4 34.4 35.0 %

Heat for Copper 60.8 120.4 0.0 67.2 kW

Heat for HLT 69.4 0.0 124.9 76.5 kW

Heat for Absorption 50.1 55.8 54.2 -- kW

Total Heat from exhaust + cooling water 180.3 176.2 179.1 143.7 kW

System Efficiency 86.09 84.91 85.74 76.23 %

Heat to Power ratio 1.50 1.47 1.49 1.17

Fuel Oil Results

Better as a CHP system for overall efficiency and savings

Higher CO2 emissions than other cases

Emits SO2 – toxic with water

Analysis – Biogas

• Case 1 has highest efficiency – also most expensive

• Complexity of system is high and may not be worth the capital investment

• Case 4 has very high efficiency and reduces need for expensive absorption unit

• AD required for both systems – increasing capital costs & complexity

Analysis – Biodiesel

• At full load could be very efficient system

• No need for AD on site so reduces capital costs

• Large amounts of energy lost if running one process at a time

• CHP system reduces waste and need for absorption

• Issues of using waste vegetable oil as fuel

• Lower emissions than other systems

Analysis – Fuel Oil

• Much simpler system – requires less capital investment and change to infrastructure of brewery

• Removes need for AD and waste oil collection

• However has lower efficiency than the other systems

• Increased emissions of SO2 and CO2

• Higher overall emissions

Conclusion

• The best overall system is Case 1 – highest efficiencies and overall savings

• Uses waste products to produce fuel generating a larger saving

• Requires the largest capital investment

• Energy model used in audit needs to be more accurate – if run 24/7 lot of energy will be wasted

• CHP system would fit model better

• Best design for brewery – Case 4

Thank You

ANY QUESTIONS??

• Acknowledgements: – Yaodong Wang

– Matthew Butcher

– Nadia McPherson

design & analysis of a biogas fuelled trigeneration system for … · 2012-05-08 · biogas...

Documents