Propane blending system for biomethane to grid applications
Low cost propane blending system for biomethane to grid schemes, transfer of technology from other industries.
Project code: OIN001-011 ISBN: ce]
Research date: 2013 Date: 2013/14
Propane blending system for biomethane to grid applications 4
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Document reference: [e.g. WRAP, 2006, Report Name (WRAP Project TYR009-19. Report prepared by…..Banbury, WRAP]
Written by: Terry Williamson, CNG Services Ltd
Front cover photography: Gas ring
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Propane blending system for biomethane to grid applications 4
Executive Summary
There exists an opportunity for the supply of a low cost propane blending system for biomethane to grid schemes which are to inject into the 2 Bar gas grid. This includes the majority of small scale projects which can be expected to have a biomethane flow of less than 100 Sm3/hr (at 1013 mB and 15°C) and be located close to a two Bar grid.
Propane blending systems require good accuracy coupled with excellent reliability. They operate within UK ambient temperatures (-20 to + 45 oC) and to stable operating conditions. Traditionally they use high value components manufactured in relatively low volumes that need to be carefully assembled and tested by trained staff.
Automotive products also require good accuracy with excellent reliability but within an extreme environment involving significant temperature swings (-40 to +120 C under bonnet temperatures) and highly cyclic duty cycles with significant resistance to impact. Traditionally they use components robustly built to a highly competitive price in large volumes. Components are available conforming to EU standards R67, R110 and ISO 15500.
This project explores the potential of using automotive parts to construct a propane blending system for anaerobic digestion facilities operating a biomethane to grid process. By using parts from an industrial environment the project will take advantage of high quality parts which are at a very low cost. The systems may be compact (designed to fit under the bonnet of the average car) and easily assembled using components rated at the expected gas pressures involved.
The final innovation is to use the expensive Programmable Logic Control (PLC) installed as part of the gas quality monitoring scheme in the entry facilities to provide control on the rate of propane injection.
Utilising automotive components and an existing PLC reduces the cost for the propane injection system to around £20k from the current £80 - £100k and represents a significant cost reduction that can help the economics of small scale biomethane to grid projects
Propane blending system for biomethane to grid applications 4
Contents
1 Introduction and background 4
1.1 The issue 4
1.2 Objectives 4
1.3 Introduction 4
1.4 Project explanation 5
1.5 Company description 5
2 Technical appraisal and Phase 1 methodology 5
2.1 Biomethane and the gas grid 5
2.2 Propane storage 6
2.3 Propane blending system 6
2.4 Development of an automotive component-based system 8
2.5 Technology considerations for Phase 2 10
2.5.1 Identified risk - Non-compliant with ATEX No 1 (EX rating) 10
2.5.2 Non-compliant with ATEX No 2 10
2.5.3 System pressures 10
2.5.4 Component durability 11
2.6 Laboratory testing 11
2.6.1 The laboratory unit control system 12
3 Preparations for Phase 2: Demonstration of the propane blending system 12
3.1 What we need to do in Phase 2 13
3.2 Mass balance 13
4 Legislation 14
5 Commercialisation 14
5.1 IP 14
5.2 Commercialisation plans 15
5.3 Manufacturing plans 15
6 Conclusion 15
7 Phase 2 Demonstrations 17
7.1 Objectives 17
7.2 Methodology 17
7.2.1 Summary of activity 17
7.2.2 Project Milestones 17
7.3 Stakeholders 17
7.4 Project Timescale 18
7.5 Economics 19
7.5.1 Project costs 19
7.5.2 Financing 20
7.6 Evaluation and monitoring 20
7.7 HSE 20
Appendix 1 Calculations 21
Appendix 2 23
A2.1 Component evaluation 23
Appendix 3 Properties of propane 25
Appendix 4 P&ID gaseous phase propane blending system 26
Appendix 5 Propane blending system control description. 27
A5.1 Overview 27
A5.2 Propane blending 27
A5.3 Temperature control and vaporisation 28
A5.4 Pressure control 28
A5.5 Temperature control 29
A5.6 Functional control 29
Appendix 6 References 30
A6.1 Part 1 - Gas industry 30
A6.1.1 Legislation 30
A6.1.2 Gas distribution network specifications 30
A6.1.3 British Standards 31
A6.1.4 European standards 32
A6.1.5 Institution of gas engineers and managers publications 32
A6.2 Part 2 - Automotive, industrial engine 33
A6.2.1 Legislation 33
A6.2.2 Environment 33
A6.2.3 European standards 33
A6.2.4 International standards 33
Appendix 7 Typical automotive LPG components 34
Appendix 8 Product costs for commercialisation 40
List of figures
Figure 1 Propane blending gaseous system. 7
Figure 2 Propane blending liquid injection system. 7
Figure 3: Capex of Clean-up system 8
Figure 4: Project timescale 17
List of tables
Table 1: Electrical Energy Consumed by the Control System 13
Table 2: Propane blending system costs 15
Table 3: Project costs 18
Table 4:Project cost sharing 19
Table 5: List of devices to measure and control 27
Glossary
AD
capex
CHP
CV
LPG
Ofgem
opex
Sm3/hr
VP
1 Introduction and background
1.1 The issue
The capital costs for construction of an anaerobic digestion (AD) plant, the upgrading of biogas to biomethane and delivering that biomethane to the gas grid are expensive operations. To make them more affordable and sustainable in the long term without resorting to subsidies requires that capital and operating costs are reduced. For a small project e.g. 100 Sm3/hr of biomethane, the propane blending plant represents around 75% of the overall Biomethane to Grid Capex and hence a reduction here will be of particular benefit. Transferrable technology also offers a way forward for the industry as a whole, and can provide more competition which will reduce the cost of propane.
Propane blending systems are offered by most of the biogas upgrading plant manufacturers and UK LPG suppliers, Calor, Shell and Flogas. However, in the biomethane market, only Flogas is active in UK projects. Flogas offers both gaseous and liquid blending systems at a cost of some £80,000 to £120,000 excluding the cost of the storage tanks. This project is reviewing the scope of reducing the cost of such systems by utilising mass produced components.
1.2 Objectives
Traditional equipment to measure and blend propane into a biomethane stream to enhance the CV of the gas is based on components designed and constructed for the process and gas industry. They are robust and durable, but expensive, primarily due to the relatively low production volumes. The objective of this study is to identify components and methods used in the automotive industry for the purpose of constructing a propane blending system. That system will offer similar performance to traditional blending systems while taking advantage of substantially reduced component costs. To achieve the objective three primary areas will be addressed in the feasibility study, namely:
· Determining the technical needs of the system
· Assessing the suitability of the identified components and their impact on overall system cost
· Outlining the requirements for market acceptability in terms of testing and validation
1.3 Introduction
LPG (a blend of propane and butane) has been used in the automotive, off highway (fork lift truck) and stationary engine industry for over 80 years. Its evolution has produced components that are safe and dependable at very low cost in huge quantities in all major countries of the world.
In industry, LPG is used to raise steam and for process loads where there is no natural gas available. In the domestic market, LPG is widely used for heating and cooking in areas where there is no gas grid or for portable equipment.
A typical flow weighted average CV for the gas grid is 39 MJ/m3. The CV of 98% methane (typical biomethane) is 37.0 MJ/m3. To increase the CV of the biomethane to the grid average, as required by Ofgem, thus requires around 10% propane energy. There are three costs associated with this:
· Propane control computer and injection system (capex)
· Propane storage (capex)
· Propane value loss (opex) - being the difference between the cost of propane and its value as natural gas
This project aims to reduce the cost of the propane control computer and injection system from £80K to around £20K with no loss of accuracy and reliability.
1.4 Project explanation
DIAD Round II aims to bring innovative technologies to the AD sector so they can be adopted by new and/or existing AD plants. The programme is focussed on the following four work streams:
1. Scaling Technology
2. Processing and enhancing digestate
3. Using Heat from AD
4. Proof of Market, AD Technologies
The overall objective of the DIAD programme is to challenge the cost of AD operations and introduce new technologies to improve operational efficiencies and costs.
This project is a technical review looking at a theoretical functional design for a system based around some key automotive components with the addition of process components where automotive parts are not available. The study scopes the components, design and relative sizes to see where it fits into the biomethane to grid industry and identifies what gas grid pressures and flow rates it can accommodate.
1.5 Company description
CNG Services Ltd (CSL) is a leading company in the AD and biomethane industry providing engineering services in relation to the development of new anaerobic digester projects including; electricity generation via CHP, clean-up of biogas to produce biomethane and its injection into the gas distribution network and use of compressed biomethane as a vehicle fuel.
2 Technical appraisal and Phase 1 methodology
2.1 Biomethane and the gas grid
Biomethane is predominately methane with some inert gasses (carbon dioxide (CO2), Nitrogen (N2) and Oxygen (O2) etc.); its gross CV is typically in the region of 36 to 37 MJ/Sm3 (at 1013 mB and 15°C)
The UK gas grid has a CV range of between 37.5 and 43 MJ/Sm3 so when injecting biomethane it will always require its CV to be enhanced to match the CV of the grid. There are exceptional circumstances when this may not be necessary due to blending but in most cases enrichment is required.
CV enhancement is achieved by blending a controlled volume of propane, the CV of which is typically 92 MJ/Sm3 with the biomethane. Typical blending quantities are some 4% by volume or 10% by energy.
Gas grids are arranged in a series of pressure tiers, each system supplying a lower pressure tier down to the point of delivery to an industrial or domestic system.
UK pressure tiers are as follows:
· LP Low Pressure, 100 mBar or less
· MP Medium Pressure, 1 to 2 Bar
· IP Intermediate Pressure, 4 to 7 Bar
· LTS Local Transmission System, 10 - 40 Bar.
Most biomethane to grid systems currently under development fall into the MP and IP pressure range, the majority being MP. For the purpose of this study the 2 and 7 Bar pressure levels only will be considered.
For injection into the LTS there is a compressor after the propane injection system and hence there is never a requirement to inject propane into a biomethane stream at >7 bar.
2.2 Propane storage
Storage vessels for this system are usually bulk refillable tanks from 1 tonne capacity upward and are sited above ground or sometimes buried. Above ground tanks are exposed to UK weather so a range of temperatures of – 5°C to + 40°C are considered (the + 40°C considers the impact of solar gain heating the tank). Buried tanks will have a lesser variation so we could consider + 5°C to + 25°C, this falls within the above ground storage so we will work with the – 5°C to + 40°C range.
Propane storage temperatures are important in that they set the in-tank vapour pressure (VP) likely to be seen. Referring to the chart in Appendix 3 we can see that at – 5°C (268 K) VP is 4.2 Bar and 40°C (313K) VP is 15 Bar. Understanding the VP is important in that it is the pressure available to push liquid propane out of the tank towards the blending system. If the pressure required at the delivery point is above the tank VP then additional measures are needed to deliver propane. We could heat the tank with hot water to raise the temperature (and the VP) or use a mechanical pump. Hot water would be preferred as this is often available as a waste energy within other parts of the system.
Low pressure systems (< 2Bar) are unlikely to require additional propane heating or pumping but to achieve an in-tank VP of 8 Bar (to allow a margin for downstream processing) it requires a temperature of 290K (17°C), so heating or pumping would be needed some of the time.
Propane is delivered by a pipe, sized to cope with the expected flow rate at minimum VP to the main system.
2.3 Propane blending system
Existing systems are mainly based on the concept of taking liquid from a storage tank, vaporising (turning the liquid into a gas) it in a heated chamber using electrical elements or heat from a source such as the cooling water system of a compressor and delivering it to a mixing chamber in through a control valve. Biomethane CV is measured upstream of the mixing chamber, the required volume of propane to be introduced is calculated and the quantity of propane flowing to the mixer is measured. The control valve responds to the measured amount in order to introduce the correct volume. Temperatures and pressures are taken into account to compensate for variations. Gas CV is measured again downstream of the blending unit and compared with a target value, any difference is fed back to the control system and propane flow is adjusted.