PDS - Design of Fuel, Industrial and Medical Gases

A few tips for compressed air design:

• There should be 2 compressors, make sure one at least is with variable speed drive (lead) and sequencer
• The dryer should be selected by compressor supplier – ideally as a package – and with bypass around the drier.
• Would recommend adding a meter to measure usage and detect leakage.
• Generous size pipework allows to deal with spikes- and acts as a reservoir
• Pipes to be laid to falls to low points with traps – and make sure there are floor drains in the location to be able to drain these to via traps
• There needs to be a safety valve from the reservoir tank to outside – well supported to prevent damage – serious forces if it operates.
• Add bypass to reservoir to allow for inspections without shutting down the system.

Compressors when design in laboratory applications will likely be of a higher quality than for workshop applications as laboratory applications will probably necessitate an oil free installation..

Also workshops will probably require a lower level of filtration but have a larger receiver as workshop loads, if used for power tools, will be quite “spiky” compared with a laboratory.

There may not be a requirement for driers or a different type of drier could work (work shop application)

The standards for different applications are defined in ISO 8573. Laboratories will general require class 1 air (possibly not with a -70C dewpoint). Workshops more likely to be a class 4 or 5 – you should agree this with your client

Medical air is produced at a nominal pressure of 4 bar (400kPa) and surgical air at 7-9 bar (700-900kPa). Typical receiver pressures vary between 9.5 and 12.5 bar.

A plant of the above type is used to supply a 700 kPa surgical air system. The requirements at the terminal unit now stand at 350 l/min at the front of the terminal unit i.e. delivered flow. Given pressure drops across terminal units and pendant hoses, a dynamic pressure of about 8 bar and a static pressure of about 9 bar are required at the rear of the terminal unit.

Given pipeline pressure drop allowances a plant output pressure of about 9.5 bar (dynamic) would be required to guarantee the terminal unit flow. Many installations use a pipeline pressure of 10-11 bar, with local pressure regulation (adjacent to theatres), adjusted during commissioning to give the required terminal unit performance. Such a system requires a typical receiver pressure of between 12 and 13 bar.

Assignment Guidance notes

Recap Exercise

Task 1

• Create 3 headings (fuel, medical & industrial)
• List the gases for each heading
• From each list pick two gases and explain the chemical composition and examples of 'real world' application
• For fuel gases evaluate which gas would be most suitable for the assignment design brief

Hand in date

Unlike natural gas, propane is heavier than air (1.5 times as dense). In its raw state, propane sinks and pools at the floor. Liquid propane will flash to a vapour at atmospheric pressure and appears white due to moisture condensing from the air.

When properly combusted, propane produces about 50 MJ/kg. The gross heat of combustion of one normal cubic meter of propane is around 91mega joules

Propane combustion is much cleaner than gasoline combustion, though not as clean as natural gas combustion.

Natural gas (methane) is the most common fuel gas, but others include:

• Syngas
• Propane,
• Butane
• Re-gasified liquefied petroleum gas
• Wood gas
• Producer gas
• Water gas
• HCNG
• Town Gas

Uncompressed Hydrogen or compressed hydrogen may be used as a fuel gas

Coal gas or Town gas, In British usage, coal gas specifically means gas made by the destructive distillation of coal.

The term is not applied to other coal-derived gases, such as water gas, producer gas and syngas. United States usage may be different. Coal gas was introduced in the UK in the 1790s as an illuminating gas by the Scottish inventor William Murdoch and became very widely used for lighting, cooking, heating and powering gas engines.

Parameters

Evaluate the properties of common fuel, industrial and medical gases (P4.1)

The image below is a schematic block flow diagram of a typical natural gas processing plant. It shows the various unit processes used to convert raw natural gas into sales gas pipelined to the end user markets.

The block flow diagram also shows how processing of the raw natural gas yields by product sulphur, by product ethane, and natural gas liquids (NGL) propane, butanes and natural gasoline

Activity

Below is a chart showing the main properties, hazards, precautions and uses of a range of medical gases:

Review legislation and design standards for fuel, industrial and medical gases, vacuums and compressed air installations (P4.2)

Assignment 4

Gas

• For each category list the applicable legislation and design standard
• Pick one legislation document and one design document - summarise in a short paragraph its purpose and content - In your own words!
• Pick one requirement from legislation and one design recommendation - give specific examples!

Applicable regulations and legislation

Refer to design guide handout

refer to handout

This list is not exhaustive you must for your assignment carry out you own research?

Applicable regulations and legislation are as follows:

• The Work in Compressed Air Regulations 1996 http://www.legislation.gov.uk/uksi/1996/1656/contents/made
• Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 1995(5) (RIDDOR)
• Pressure Systems and Transportable Gas Containers Regulations 1989(10).
• Health and Safety at Work etc. Act 1974(2)

Design Guides & Standards

Applicable regulations and legislation

• Health and Safety at Work etc. Act 1974(2)
• Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 1995(5) (RIDDOR)
• Pressure Systems and Transportable Gas Containers Regulations 1989(10).

Applicable regulations and legislation are as follows:

• Gas Safety Regulations 1972(1): cover the gas main up to the service cock
• Gas Safety (Rights of Entry) Regulations 1996(3)
• Gas Safety (Installation and Use) Regulations 1998(4) cover service pipework
• Gas Act 1995(6)
• Offshore Safety Act 1992(7)
• Gas Appliance Directive 1992(8)
• Gas Appliances (Safety) Regulations 1995(9) (support the Gas Appliance Directive 1992)

http://www.igem.org.uk/technical-standards/standards.aspx

This list is not exhaustive you must for your assignment carry out you own research?

Medical gas

Design Fuel, Industrial and medical gas, vacuum and compressed air installations for buildings, P4.3

Throughout healthcare premises there is a need for a varied amount of medical gases. Below is a list of gases supplied via pipeline systems in the establishments:

The above drawing and picture demonstrates a compressed gas cylinder manifold system. These systems are used to supply oxygen, medical or air surgical, air nitrous oxide, oxygen/carbon dioxide mixture or entonox/equinox.

Industrial gas

A typical vacuum system extracted from an Eastwood park training book.

Medical vacuum systems are designed to produce a vacuum of 300 mmHg (kPa) at flow rate of 40 litres per minute at the most remote terminal unit. In reality flow rates are commonly far lower than this, typically around 6 litres per minute.

Liquid Petroleum Gas LPG

Schedule 2

LPG installations are covered by BS5482: parts 1,2&3

LPG is stored in tanks that range in size from domestic 1/2 tonne to commercial 113,5,7 and 12 tonne tanks

Another method of sizing tanks is to use their water capacity i.e. 450 litres

Fuel gas

Also refer to Calor Gas brochure

(separate hand out)

Propane / Butane Cylinders

Schedule 1

Follow on Exercise:

A small office block has a 50kW gas boiler & a ‘six hob’ gas cooker. Determine the total flow rate & pipe size if the distribution pipe totals 30m from the meter & the pipe work losses should not exceed 1mbar

1mbar = 100 Pascal's = 0.01mh

Specific gravity of gas, S = 0.6 m/s2

for the assignment brief Assume 3 Gas Boilers & 3 Bunsen burners

Gas Safe Interlocks

Natural gas

Gas pipe sizing

For volume flows up to 160 m3/hr ( ~ 1750 kw /hr ) a diaphragm meter may used. However, this is a bulky meter and two to three times more expensive than an equivalent rotary meter. If the turndown ratio is not critical, especially if there is a space limitation, a rotary meter may be used. Example :- a gas supply a workshop with four 60 kw radiant heaters each controlled with an on / off thermostat then a rotary meter would be applicable.

The pressure drop across s the meter is also important, A 100mm pipe may be able to supply two boilers rated at 750 kw input, however the pressure drop across a 100mm meter located in the basement was sufficient to breach the Gas Safety Regulation for the boilers located five storeys above on the roof. Instead the 100mm was removed and an 80mm meter was installed adjacent to each boiler.

An alternative for very low gas flows is a Rotary Piston meter (such as the Delta QD). They have been especially designed for industrial use and for secondary measurement and are particularly adapted when the flow can be low or irregular. ( Model QD25 1 to 25 m3 / hr and the QD60 2.5 to 60 m3 / hr )

Diaphragm meter

Rotary meter

Gas Sub-metering

Extract from Institute for Plumbing

Diaphragm meter pressure drops

The selection of the correct type of gas meter and ancillary equipment is important otherwise some of the gas usage may not be monitored. The type of meter selected will depend on

•Minimum and Maximum Flow

•Turndown Ratio

•Type of gas equipment ( lab bench equipment, boiler load, catering equipment, laundry equipment, workshop equipment / furnace / kiln )

For low volumes of gas usage ( laboratory Bunsen Burners, Laundry Tumble Driers ) for accurate monitoring a positive displacement ( Diaphragm ) meter must be used.

Gas Schematic

Positive displacement meter

To monitor the pulse output from any fiscal gas meter, a Chatter box or ATEX approved radio device has to be installed.

Approx £ 600 +Vat to install a chatterbox and pulse output cable.

•Pulse Output 1 will provide a connection for the gas supplier device to provide a monthly remote to import into their billing system.

•Pulse Output 2 is provided for daily monitoring of Interruptible gas supplies and large Firm Gas Supplies in excess of 250,000 BTU (Therms). 1000BTU = 0.3 kWh

•Pulse Output 3 is provide to connect the customers Energy Management System for live data usage display.

Ventilation

Fiscal Meters

All this can be automated in an excel spreadsheet to speed up the calculation

CIBSE CPD

Opportunities for higher award:

Discuss 1mbar 'system resistance' how would you interpret this wording? how easy is this to achieve??

Gas mains in the united Kingdom fall into the following types:

• Intermediate pressure mains operating between 2 and 7 bar and constructed from either steel or polyethylene pipe.
• Medium pressure mains operating between 75mbar and 2bar and constructed from either steel. polyethylene, cast iron or ductile iron pipe.
• Low pressure mains operating at approximately 30mbar and up to pressures of 75mbar and constructed of polyethylene, cast iron or ductile iron pipe.

Determine permissible Pipework losses

Now work out the permissible pressure loss for gas pipework. This is the limiting criteria for pipe sizing!

Use Equivalent Length method for fitting loss i.e.

+30% for fittings

(+30% for tracpipe < 32mm, +10% < 50mm)

1mbar / equivalent length of pipe

Produce schedules for the commissioning, testing and purging of fuel gas installations, P4.5

Perform calculations to size, select and specify pipework, plant and equipment sizes for fuel gas installations, P4.4

External mains

The selection of the correct type of gas meter and ancillary equipment is important otherwise some of the gas usage may not be monitored. The type of meter selected will depend on

•Minimum and Maximum Flow

•Turndown Ratio

•Type of gas equipment ( lab bench equipment, boiler load, catering equipment, laundry equipment, workshop equipment / furnace / kiln )

For low volumes of gas usage ( laboratory Bunsen Burners, Laundry Tumble Driers ) for accurate monitoring a positive displacement ( Diaphragm ) meter must be used.

An alternative for very low gas flows is the Delta QD Rotary Piston meter. They have been especially designed for industrial use and for secondary measurement and are particularly adapted when the flow can be low or irregular. ( Model QD25 1 to 25 m3 / hr and the QD60 2.5 to 60 m3 / hr )

For volume flows up to 160 m3/hr ( ~ 1750 kw /hr ) a diaphragm meter may used. However, this is a bulky meter and two to three times more expensive than an equivalent rotary meter. If the turndown ratio is not critical, especially if there is a space limitation, a rotary meter may be used. Example :- a gas supply a workshop with four 60 kw radiant heaters each controlled with an on / off thermostat then a rotary meter would be applicable.

The pressure drop across s the meter is also important, A 100mm pipe may be able to supply two boilers rated at 750 kw input, however the pressure drop across a 100mm meter located in the basement was sufficient to breach the Gas Safety Regulation for the boilers located five storeys above on the roof. Instead the 100mm was removed and an 80mm meter was installed adjacent to each boiler.

On the advice of Transco all sub gas meters should be installed with a chatter box, approved ATEX radio device or galvanic isolation device

For radio communications the university uses the best practise method adopted for the gas industry. A chatterbox will be installed to each sub meter ( Dresser 103-e ) interposed between the pulse output and the connection to the metering system using a non ATEX radio device or hard wire connection to a data logger.

Gas Sub-metering

Positive displacement meter

Size key components

Gas Schematic

Meters, solenoid valves and pipework all add a resistance to the system.

Meters should be selected to achieve optimum accuracy at minimum resistance

Pipe work (including bends and isolation valves) should be sized not to exceed 1mBar

Gas pipe sizing

Now work out the permissible pressure loss for gas pipework. This is the limiting criteria for pipe sizing!

available / equivalent length of pipe

Assess loads & pressure

Pressure losses

Available pressure = 21mBar

Gas boilers require 18mBar

therefore 3mbar pressure is spare!

(1mbar = 100 Pascal's = 0.01mh)

Exercise:

A small office block has a 50kW gas boiler & a ‘six hob’ gas cooker. Determine the total flow rate

Boiler output (kW) * 3600 / boiler efficiency / calorific value of gas = m3/h

Calorific value of gas (kJ/m3) = 37500,

Sketch out system

Break the task into three headings

Gas:

Provide a simplified schematic showing meters, SV, purge points and indicating pipe sizes a short paragraph for the following:

• which type of meter you would select and where and why
• any ventilation requirements you have identified
• justify your pipe choice (refer to next task)
• what safety measures / devices are required & where

Industrial gas:

• Provide a simplified schematic of a compressed air installation

Medical gas:

• Provide a simplified schematic of either a oxygen or nitrogen system and a vacuum system

Provide a short paragraph for the following (in your own words) why do we need to test,

why we purge and, why we commission a fuel gas system.

Also schedule out the flowrates to each appliance in you design & the minimum pressure required.

Also fill out schedules 1 & 2

Provide pipe sizing spread sheet and one hand calculation to validate our answer

Provide manufacturers data sheet for gas meter with your flow rate marked up and indicating pressure loss

Provide manufacturers data sheet for solenoid valve with your flow rate marked up and indicating pressure loss

For higher award:

comment on the gas sizing guidance, is there conflicting guidance? opportunity to be critical of guidance or your approach, don't forget to validate / justify your approach or conclusions.