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ASHRAE January 10, 2017

Steam Properties, Production, and Uses

Kevin Foley Chief Engineer and Property Manager

Lowell General Hospital

MA 1st Class Steam Engineer, BSME, CEM, CHFM

Presenter

• MA 1st Class Steam Engineer

• BSME – UMass Lowell

• Certified Healthcare Facility Manager

• Certified Energy Manager

• 30+ Years in Steam and Power Generation:– Industrial/Healthcare/Food and Beverage/Tech.

– Utility Sized Combined Cycle – Gas Turbine and Steam Turbine

– Cogeneration – (“waste” thermal energy is used)

– Natural Gas, Coal, Tires, Rice Hulls, Trash

• National Association of Power Engineers Past President and Lifetime Member

ASHRAE Guide

• FUNDAMENTALS OF STEAM SYSTEM DESIGN– Self-directed Learning Course

– 236 Pages• Chapter 1. Introduction to Steam System Design

• Chapter 2. HVAC Steam Systems

• Chapter 3. Terminal Units I [heaters]

• Chapter 4. Terminal Units II

• Chapter 5. Boilers

• Chapter 6. Steam Valves, Steam Traps, Flash Tanks, and Condensate Receiver Tanks

• Chapter 7. Steam Piping Design

Steam Properties

– Steam is a gas at defined pressures and temperatures and some examples are: • 0 PSIG - 212⁰ F

• 10 PSIG - 239⁰ F

• 150 PSIG - 335⁰ F

• 3200 PSIG - 696⁰ F

– Steam exists as low as 32⁰ F - in a perfect vacuum

– Steam is the same density as water at 3,206 PSIG• Super High Critical Boilers operate in this range

– Normal speed in pipe is 80 ft/s – 55 MPH

Steam Properties Continued

– Steam Pressure corresponds to a temperature in its “saturated” state

– Steam contains energy added in several steps1. Portion greater than 32°F or starting temperature. – if

condensate is returned at 140°F you need to add the energy to raise the temperature to the boiling point.– adding 1 BTU per lb to water increases it temperature 1°F – Example: you have to add 108 BTUs to 1 lb of water to raise its

temperature from 32°F to 140 °F

2. Latent Heat of Evaporation – conversion from water to Steam (and you have to remove the same energy to change it back)

3. Superheat to raise the temperature

– Enthalpy is the amount of heat in steam in BTUs

Steam Properties Continued

• Water expands 1,600 times in the conversion to gas “steam”– In the atmosphere this is the plume that we see– In a pressurized vessel full of hot water the same

expansion takes place if the pressure is suddenly dropped -leading to explosive pressures and possible rupturing of pipes and tanks. • Example – weekend shutdown in a factory where a main steam

line trap failed and condensate filled the steam line. The Monday morning startup steam flow created a large pressure drop and the condensate at 335⁰ F flashed into steam and ruptured a 12” steam main for about 18”.

• The lab estimated the pressures exceeded 4,000 PSIG • Boiler Explosions are catastrophic because of this expansion rate

Steam – Ruptured Pipe

Boiler Pressure Vessel Explosion

Saturated Steam

• Saturated Steam - Steam is “saturated with energy”– If you add (1) more BTU the temperature will rise above the

corresponding temperature in the steam table and the steam will become superheated

– Steam can be saturated and dry

– Steam Quality less than 100% is “wet”

– Steam Quality Measurement is complicated – you need an Isokinetic probe to take samples and specialized metering.

– Saturated Steam Meters apply a Steam Quality factor – say .98

– Steam can be Saturated from perfect vacuum to Supercritical

Superheated Steam

• If you add any more energy to saturated steam – even by just 1 BTU the temperature will rise above the temperature for the corresponding pressure

• Example: • Saturated Steam @ 650 PSIG Steam is 497 °F contains 1,202 BTUs per pound.• Superheated Steam @ 650 PSIG and 740° F contains 1,678 BTUs per pound

• Superheated steam is used where dry steam is needed through an entire process - Steam Turbine and Engines need superheated steam and very long runs of piping.

• Superheating steam improves the processes thermal efficiency - most BTUs put in can be taken out as the Latent Heat of Evaporation has already taken place.

• Superheating is accomplished by running steam that has left the boiler through another heating section in the boiler casing or a separately fired heater.

• Running steam through a PRV can generate some superheat by reducing pressure and holding the temperature constant.

Steam Tables – in PSIA

Steam Production

WaterTube BoilerPressure Vessel Watertube Boiler Finished

Steam Production ContinuedFireTube Boiler

Pressure Vessel Firetube Boiler Finished

Steam Production Continued

HRSG HRSG Tube

13X the area of a bare tube

Steam Production

Utility Boiler Nuclear Reactor

Steam Uses

• Heating - Coils, pipes, hoses• Cooling – Absorption Chillers• Mechanical/Physical use

– Steam Turbines – Pumps, Compressors, Generators,– Steam Turbines - Ships/Submarines for generators and

propellers – Steam Engines – Still in use– Simplex and duplex pumps– Aircraft Carrier Catapults – Humidification – Cleaning

Steam Uses - Continued

• Thermal:

– Sterilization – Hospitals

– Manufacturing parts – Steam quickly melts out wax in investment castings

– Kitchens - Kettles

– Large Scale cooking – Retort Ovens and Blanchers, bakeries – prevent bread from bursting

– Generate vacuum – for processes and cooling

• Cools 1 Ton of cooked potatoes in 40 minutes

Steam Turbine

Steam Turbine RotorBlades/Buckets

Steam Retort Cooker

Cooks Tons of vegetables

Steam Continuous Cooker

Steam Venturi for Vacuum

Venturi Principle Venturi

Steam – How it works• Useful energy available to do work is the amount of energy

used to raise the temperature to the boiling point, the Latent Heat of evaporation and the energy to Superheat Steam:– Sensible Energy used to raise water to the boiling point.

• ex. @ 650 PSIG @ 497°F (497°F- 110°F) = 387 BTUs

– Latent Heat of evaporation:• 970 BTU’s per pound at 0 PSIG• 881 BTU’s per pound at 100 PSIG• 717 BTU’s per pound at 650 PSIG (Saturated or Superheated)

– Superheated Steam Enthalpy above Saturated• 173 BTU’s per pound at 650 PSIG and 750°F

– Total Energy Available Example @ at 650 PSIG and 750°F:• (497-110 = 387) +717+173= 1,277 BTUs per lb

Steam Plant Maintenance• Daily Low Water Cutoff and Alarm testing – ensures the boiler will shutdown if there is no

water

• Boiler Water Chemistry

– Feedwater pre-treatment – softeners, demineralizers, RO

– Water Treatment Vendor – Service and Chemicals

– Chemicals can also be injected into steam lines and condensate reeivers

– I have minimized or eliminated automated chemical controls where boiler operators are available

– Daily checks by operators and monthly checks by 3rd party is an industry standard

– Commercial building steam or hot water systems - $100/month per building for a Water Treatment Vendor is a reasonable investment for your assets

• Safety Valve Maintenance – lift annually and rebuild every 3-5 years

• Annual Boiler Pressure Vessel inspections

– By Insurer in most states

– By the State if there is no insurer - in ASME states

– Clean the water and fire side surfaces as needed – saves money and cleanliness can be monitored by watching the exhaust temperature

• Annual Boiler Tunes ups for efficient Combustion required by EPA/DEPs – this saves $$

• Annual Boiler Combustion Device Inspections

– Low Water cutoff, Gas/Oil/Air pressure witches, Gas Valves, Flame detectors

Boiler Water Chemistry• FDA and Non-FDA programs• pH of 9-11

– Usually add Caustic Soda (Sodium Hydroxide) and/or use Mono, Di or Tri Sodium Phosphate• Mono-Sodium Phosphate – lowers ph• Di-Sodium Phosphate – pH neutral• Tri-Sodium Phosphate – Increases pH

– High pH may lead to Caustic Embrittlement

• Dispersant – keeps solids in suspension to be blown down• Amines – designed to leave with the steam and adjust pH

of the condensate as the steam condenses – Types depend on the system size and distance from the boiler

Steam Line Maintenance • Steam Traps – PM Saves $$$$

– Energy($) blows through a leaking trap without doing any work– MassSaves pays 100% of annual surveys and 50% of repairs - Payback is in months– Prevent water hammer – steam at >>> 80 ft/sec on start up will push water right through 90’s,

valves, strainers… rupturing them and causing significant losses or even injury or death.– Prevent flashing discussed earlier

• Pipe and Boiler Insulation– Type and protection from environment

• Wet location?• Abuse – workers, forklifts, washable?

– Terminal thickness – there is a point where there is no benefit to adding more insulation– MassSaves now pays 100% for insulation repairs - Insulation vendors will come back annually

and inspect and replace insulation blankets that were removed and not put back– Corrosion Under Insulation “CUI” is a big concern – water gets under and rusts causing pitting

• Hangers – always overlooked. – Loose nuts on threaded rods and hangers– Creep – the hangers move along the pipe during start up and shutdown and away from

hanging plumb.– Rust and damaged – forklifts push up and bend the rods

• Ultrasonic Thickness testing on older pipe and welds – especially at turns

Water Hammer

• Water Hammer 1 – Condensate moving at a high speed bursting through turns or fittings

• Water Hammer 2 – Steam contacting cold or cooler condensate– Steam condenses as it contacts water/condenate– The steam volume decreases 1600 times– Water rushes in and makes a pinging sound – and in severe

cases can shake piping or tanks

In both cases – start-up drains discharging to the floor and/or drain are used to supplement traps and are operated manually by the boiler operators and can be used when traps fail

Steam System Design1. Determine the process temperature2. Determine the heat load – Convert to steam flow3. Determine the location of the boilers in relation to the process4. Using Items 1, 2 and 3 - determine the pressure and temperature (superheat?)

1. High or Low Pressure Steam – Boiler Operators needed?2. Initial Pipe size

5. Select Boilers - Using Item 41. Watertube vs. Firetube or Field Constructed2. Efficiency – can you use an economizer to heat the feedwater with the boiler exhaust? 3. Fuel(s)4. Permit requirements - DEP/EPA regulations

6. Determine pipe Material, size and run1. Material – based on pressure and temperature2. Pipe Size – see table3. Runs - accommodate expansion including anchors, hangers, flexible loops or joints

• Rule of Thumb for expansion – 1” per 100’ per 100°F7. Determine Steam trap location and steam trap type

1. How often is the steam system shut down – weekly vs. yearly makes a big difference on traps 2. Prevent Water Hammer 3. Place start-up drains in strategic locations

8. Determine insulation type and thickness

Steam pipe selection example: 10,000 pph at 10 PSIG and 100 PSIG

Capacity (lb/hour)

Pressure (psi)Steam

Velocity (ft/sec)

Pipe Size (inch)

1/2" 3/4" 1" 1 1/4" 1 1/2" 2" 2 1/2" 3" 4" 5" 6" 8" 10" 12"

5

50 12 26 45 70 100 190 280 410 760 1250 1770 3100 5000 7100

80 19 45 75 115 170 300 490 710 1250 1800 2700 5200 7600 11000

120 29 60 110 175 245 460 700 1000 1800 2900 4000 7500 12000 16500

10

50 15 35 55 88 130 240 365 550 950 1500 2200 3770 6160 8500

80 24 52 95 150 210 380 600 900 1500 2400 3300 5900 9700 13000

120 35 72 135 210 330 590 850 1250 2200 3400 4800 9000 14400 20500

20

50 21 47 82 123 185 210 520 740 1340 1980 2900 5300 8000 11500

80 32 70 120 190 260 520 810 1100 1900 3100 4500 8400 13200 18300

120 50 105 190 300 440 840 1250 1720 3100 4850 6750 1300 19800 28000

30

50 26 56 100 160 230 420 650 950 1650 2600 3650 6500 10500 14500

80 42 94 155 250 360 655 950 1460 2700 3900 5600 10700 16500 23500

120 62 130 240 370 570 990 1550 2100 3950 6100 8700 16000 25000 35000

40

50 32 75 120 190 260 505 790 1100 1900 3100 4200 8200 12800 18000

80 51 110 195 300 445 840 1250 1800 3120 4900 6800 13400 20300 28300

120 75 160 290 460 660 1100 1900 2700 4700 7500 11000 19400 30500 42500

60

50 43 95 160 250 360 650 1000 1470 2700 3900 5700 10700 16500 24000

80 65 140 250 400 600 1000 1650 2400 4400 6500 9400 17500 27200 38500

120 102 240 410 610 950 1660 2600 3800 6500 10300 14700 26400 41000 58000

80

50 53 120 215 315 460 870 1300 1900 3200 5200 7000 13700 21200 29500

80 83 190 320 500 730 1300 2100 3000 5000 8400 12200 21000 33800 47500

120 130 290 500 750 1100 1900 3000 4200 7800 12000 17500 30600 51600 71700

100

50 63 130 240 360 570 980 1550 2100 4000 6100 8800 16300 26500 35500

80 102 240 400 610 950 1660 2550 3700 6400 10200 14600 26000 41000 57300

120 150 350 600 900 1370 2400 3700 5000 9100 15000 21600 38000 61500 86300

120

50 74 160 290 440 660 1100 1850 2600 4600 7000 10500 18600 29200 41000

80 120 270 450 710 1030 1800 2800 4150 7200 11600 16500 29200 48000 73800

120 175 400 680 1060 1520 2850 4300 6500 10700 17500 26000 44300 70200 97700

150

50 90 208 340 550 820 1380 2230 3220 5500 8800 12900 22000 35600 50000

80 145 320 570 900 1250 2200 3400 4900 8500 14000 20000 35500 57500 79800

120 215 450 850 1280 1890 3400 5300 7500 13400 20600 30000 55500 85500 120000

200

50 110 265 450 680 1020 1780 2800 4120 7100 11500 16300 28500 45300 64000

80 180 410 700 1100 1560 2910 4400 6600 11000 18000 26600 46000 72300 100000

120 250 600 1100 1630 2400 4350 6800 9400 16900 25900 37000 70600 109000 152000

Boiler Operator License Laws

• MA – All boilers greater than 15 PSIG and 9 HP – 9-250 HP Periodic Attendance

• Daily Maintenance, Stay in same building, Auto shutdown

– 251-500 HP Non-Continuous Attendance• Same as above, Remote Station, 4-6 rounds per shift

– 501 HP and above - Continuous Attendance

• NYC – Large boilers and most turbines – utilities and high rises

• NJ – Utility sized boilers

• Connecticut, Wisconsin – large boilers

Power of Steam

• https://www.youtube.com/watch?v=jbreKn4PoAc