Adca Training. Part 1

Transcription

1 Adca Training Part 1 This presentation is only a guideline, that can only be completed by a trained personnel. (This document s total or partial use and/or reproduction is only allowed if the reference to the source is kept)

2 Part 1 Fundamentals of Steam Part 2 The Boiler Equipment Used on Boilers Water Treatment Bottom Blow down TDS Control Energy Recovery Deaerators Part 4 Pressure Reduction Safety Relief Valves and Other Steam Valves Part 5 Control Valves Components of Control Valves Humidification Part 3 Pipeline Sizing Water Hammer Steam Trapping Condensate Removal

3 Steam Feedwater Feedtank Process Condensate Boiler

4 A liquid given enough energy (heat) will break down the molecular bonds between molecules to form a gas. For water this is the transition between water and steam. Steam is a convenient and economical way of conveying large quantities of energy from one place to another. Steam is versatile and easy to control, made from a plentiful commodity: water- to which heat is added to convert it to a vapour state. Other well-known heating fluids: hot water, high-pressure hot water (superheated), low pressure high temperature heating fluids (thermal oils).

5 Amount of heat Large calorie (Kcal) is the amount of heat required to raise of 1 ºC, 1 Kg of water (from 14,5ºC to 15,5ºC). 1 Kcal = 4,1868 KJ 4,19 KJ Joule (J) The work done to produce the power of one watt continuously for one second (or one watt second). So, a KW/h (Kilowatt hour) is J or 3600 KJ. Specific heat Each body needs a different amount of heat to raise the same weight quantity by the same temperature. The amount of heat required to heat 1 Kg of a certain body by 1ºC is called the specific heat of this body ( Kcal/Kg ºC or KJ/Kg ºC)

6 Vessel water volume 5000 l 5000 Kg T=60ºC Heat content Total Heat: 5000 Kg x1 Kcal/Kg ºCx60 ºC= Kcal The amount of heat contained (stored) in a body. For example, water at 60 ºC has a heat content of 60 Kcal/Kg. or 5000 Kg x 4,19 KJ/Kg ºC x 60 ºC= KJ = 349KW

7 Pressure and Temperature are directly proportional for saturated steam. Pressure and Specific Volume of steam are inversely proportional. Pressure and Specific Enthalpy ( latent heat ) of steam are inversely proportional.

8 PHYSICAL PROPERTIES OF SATURATED STEAM Pm Gauge pressure; Pa Absolute pressure; T Temperature; V Specific volume; Pm (bar) Pa (bar) T ( C) V (m 3 /Kg ) he (Kcal/ Kg) he (KJ/Kg ) r (Kcal/ Kg) r (KJ/Kg ) hg (Kcal/ Kg) hg (KJ/Kg ) 0,00 1, ,0 1, ,1 419,1 539,4 2258,4 639,5 2677,5 0,50 1, ,6 1, ,9 468,5 531,9 2227,0 643,8 2695,5 1,00 2, ,4 0, ,8 505,8 526,0 2202,3 646,8 2708,0 1,50 2, ,6 0, ,1 536,3 521,1 2181,7 649,2 2718,1 2,00 3, ,7 0, ,4 562,7 517,0 2164,6 651,4 2727,3 3,00 4, ,7 0, ,7 605,8 509,9 2134,8 654,6 2740,7 4,00 5, ,0 0, ,1 641,0 503,8 2109,3 656,9 2750,3 5,00 6, ,9 0, ,3 671,1 498,5 2087,1 658,8 2758,3 6,00 7, ,0 0, ,7 697,9 493,8 2067,4 660,5 2765,4 he Specific enthalpy of liquid; r Specific enthalpy of vaporization; hg Specific enthalpy of saturated steam. 7,00 8, ,5 0, ,4 721,8 489,4 2049,0 661,8 2770,8 8,00 9, ,4 0, ,6 743,6 485,4 2032,3 663,0 2775,8 9,00 10, ,0 0, ,3 763,3 481,6 2016,4 663,9 2779,6 10,00 11, ,1 0, ,8 782,1 478,0 2001,3 664,8 2783,4 12,00 13, ,7 0, ,8 815,6 471,4 1973,7 666,2 2789,2 13,00 14, ,1 0, ,5 831,1 468,3 1960,7 666,8 2791,8 14,00 15, ,3 0, ,0 845,7 465,3 1948,1 667,3 2793,9 15,00 16, ,4 0, ,3 859,6 462,5 1936,4 667,8 2795,9 18,00 19, ,9 0, ,4 897,8 454,4 1902,5 668,8 2800,1 19,00 20, ,5 0, ,2 909,4 451,8 1891,6 669,0 2801,0 20,00 21, ,0 0, ,0 921,1 449,4 1881,5 669,4 2802,6 25,00 26, ,1 0, ,3 972,6 437,7 1832,6 670,0 2805,2

9 Sensible heat (heat of the liquid) The heat required to raise the temperature of a unit mass of water from freezing point to saturated temperature (boiling point). Latent heat (heat of the vapour) The heat required to convert a unit mass of water at saturated temperature to dry steam at the same temperature. Super heat The heat required to raise a unit mass of dry steam at saturation temperature to any greater specified temperature. Total heat The total heat in the steam at any time, it is the total of the sensible heat, the latent heat and the superheat.

10 Temperature ºC Saturated Temperature (Boiling point) Saturated Steam Super Heated Steam Water Heat content Sensible heat Latent heat Total heat Super heat

11 Boiling temperature in ºC (Saturated temperature) Absolute pressure in bar Boiling temperatures increase with rising pressures and drop with decreasing pressures.

12 According to previous information and at atmospheric pressure: If 1 Kg of water is heated, it s heat content and it s temperature increase simultaneously up to 100 Kcal and 100ºC, after this point if further heat is added, the heat content and temperature of the water no longer increase but the water will start to boil. Adding more heat to the water, the water is transformed from the liquid state to the gaseous state : boiling water becomes steam. From steam tables we can see that if we add 540 Kcal to the boiling water at 100ºC (100Kcal) it will became one Kg of steam with 640 Kcal heat content ( ). We can state: Heat content of water Heat content of vaporization Heat content of steam 100 Kcal 540 Kcal 640 Kcal

13 Volume Cold Water As far as steam yields it s heat, it is being retransformed from the gaseous into the liquid state, or, in other words, the steam condenses! Steam Condensate Energy For the efficient use of saturated steam it is the latent heat that does the work!

14 Vessel volume = 5000l 5000Kg Initial Temperature = 10ºC Required Temperature = 60ºC Q 5000 Kg x 1Kcal/Kg ºC x Q Kcal/h If it is required to heat the vessel content in 20 minutes, we have: 5000Kg x 1Kcal/Kg ºC x 60º-10º Q 20' Q Kcal/h How much steam? 60º-10º x 60' Steam Coil Condensate Steam NOTE: Radiation losses and vessel mass heating have been neglected.

15 How much steam? Pm Steam Pressure: 6 bar g r Latent Heat: 493,8 Kcal/Kg Kcal/h 1518,8Kg/h 493,8 Kcal/Kg Q 5000 Kg x 1Kcal/Kg ºC x 60º-10º Q Kcal/h If it is required to heat the vessel content Steam 1518,8 Kg/h in 20 minutes, we have: 5000Kg x 1Kcal/Kg ºC x 60º-10º Q 20' Q Kcal/h x 60' Condensate 1518,8 Kg/h

16 Pressure is the force that acts on a surface of 1 cm2. Under normal conditions the air pressure at sea level is 1, 033 Kgf/cm2 or 1 physical atmosphere or 1 bar. For our considerations and for simplicity reasons we will accept : 1 Kgf/cm2 as normal air pressure and 1 bar = 1 Kgf/cm2. Steam is a gas and subject to the same laws as all gases. When water is being evaporated in an enclosed limited space like a steam boiler and if it can not blow off into the open, the pressure of this steam will rise above atmospheric pressure. The pressure can be maintained at a desired level if, after having reached the required value, the heat is throttled (by firing cut off or heat source control) so that no more water is being evaporated.

17 100ºC >100ºC On the open cooker the water boils at 100ºC slowly cooking process. The closed pressure cooker aloud a more rapid cooking with a higher temperature >100ºC, consequence of the overpressure created by the formation of steam.

18 Example 1: Water to Water Heat Exchanger We need to heat 2000 Kg/h of water from 20º to 30ºC (2000 x 1 x 10 = Kcal/h). If we use hot water from a water boiler with outlet 85ºC and return at 65ºC, it means that the water yields 20 Kcal per Kg to the secondary water through the heat exchanger. In this case we need 1000 kgs of heating water every hour to replace the necessary energy ( Kcal/h : 20Kcal/kg = 1000 Kgs/h)

19 Example 1: Steam to Water Heat Exchanger We need to heat 2000 Kg/h of water from 20º to 30ºC (2000 x 1 x 10 = Kcal/h). If steam were used as heating fluid instead, at the given pressure of one bar abs, to cover the same energy demand, we would then need Kcal/h : 540 Kcal/Kg = 37 Kgs/h of steam! There would remain 37 Kgs of condensate with a heat content of 100 Kcal/Kg corresponding to a temperature of 100ºC, which returned to the steam boiler will be retransformed into steam. Going deeper to pipe sizing, different steam operating pressures, unit heater sizing, etc, more surprising differences will be found...

20 Primary Water from Boiler 1000Kg/h 85ºC 2000Kg/h 30ºC Water to water Kcal/h Heat Exchanger 65ºC Primary Water return to Boiler 20ºC Water Steam to water Steam from Boiler 37Kg/h 100ºC 2000Kg/h 30ºC Kcal/h Heat Exchanger Condensate Return 37Kg/h 100ºC 20ºC Water

21 From the steam tables we will take the following data: At 12 barg the heat content from the boiling water is 195Kcal/Kg At 0,5 barg the heat content of the boiling water is 112Kcal/Kg This means that at 12 barg each Kg of boiling water contains 83kcal more than at 0,5 barg and at a 0,5 barg the water can not hold more than 112Kcal/Kg! This liberated energy (83Kcal/Kg) produce the same effect as if an external source of energy have been added and vaporization will occur. Again, from steam tables the energy required to vaporize 1 Kg of water at 0,5 barg is 532Kcal/Kg, and so, the liberated energy will produce 83: 532= 0,156Kg (approximately 16% of the boiling water to be retransformed into steam): this is FLASH STEAM!

22 Flash in Kg per Kg of condensate Kg Pressure on traps in bar Kg 0,20 0,20 0,18 0,16 0,14 0,12 Rising steam pressure in bar 0,18 0,16 0,14 0,12 0,156 Kg (given ex.) 0,10 0,10 0,08 0,08 0,06 0,06 0,04 0,04 0,02 0, FlashSteam % he High Pressure- helow Pressure r Low Pressure 100 % NOTE: Available software SFW.FV

23 From the steam tables we can check the great volume difference between steam and water (condensate). When a heat exchanger, jacketed pan or other steam process equipment cools down there are therefore conditions for the formation of vacuum and consequently the equipments may be destroyed by implosion. ICE Steam 1,5 bar a (V=1,149m 3 /Kg) 0,174Kg of steam 0,2 m3 Barrel 200l (0,2m 3 ) Water (condensate) 1bar a 0,174Kg of water 0, m3 0,2 m3 0,000174m3

24 When the steam is turned off, air fills the void that is generated due to the condensing of the steam (otherwise vacuum will be formed). When the system is turned back on line, it is crucial that air is removed from pipes and equipment. Disadvantages of air presence on steam systems: -Air reduces the temperature of steam -Air reduces the heat transfer rate -Air and CO2 mixes with water and can cause serious corrosion problems.

25 Air Barrier Condensate Barrier Scale Barrier Metal Heat Transfer Wall Scale Product Barrier Product Barrier Heat Transfer Layers Heating steam Product or Medium Being Heated Heat Flow

26 Steam Temperature Air Barrier Condensate Barrier Scale Barrier Metal Heat Transfer Wall Scale Product Barrier Product Barrier Product Temperature Temperature Gradients Across Heat Transfer Layers T1 Heating steam Product or Medium Being Heated Heat Flow T2 T1 > T2

27 Barriers will substantially reduce heat transfer. Air, condensate and scale barriers will blanket heat transfer surface, however, air is by far the one that offer a greater resistance to heat flow. As mentioned before air enters a steam system during shut-down but it is also released when water is boiled. Since it s density it s closed to the steam under the same conditions, the air is then pushed along with steam. In any mixture of gases, each gas exerts only a portion of the total pressure based on the amount of each gas present. If we have 1/3 of air and 2/3 of steam and if the system pressure is 3 bar the steam is at 2 bar and air at 1 bar. If the system is designed for 3 bar, we can read 3 bar on the pressure gauge, but the real temperature corresponds to steam at 2 bar! To improve heat transfer efficiency it is imperative to: - Eliminate the air; - Have good condensate drainage; - Use adequate water treatment; - Have a correct equipment flow design.

28 It is evident that the condensate, air and non-condensable gases must be removed from the process equipments to assume process efficiency, keeping the heating surfaces blanked with steam. Steam naturally flows toward the cooler heat transfer surfaces, condenses into water and is carried to the drain by gravity. It is crucial to find a way to discharge the condensate (and remaining gases) without steam waste, in other words, we need to catch the steam, and for that we need a trap.

29 Steam P1=0,5 bar g Steam trapped inside the heat exchanger Heat Exchanger Condensate h1 = 5 m 5 m.c.a. Siphon h2 = 1m (1 m.c.a. = 0,1 bar g) P2 = 0,5 bar g ΔP = (P1+h2) - P2 - PERHAPS NOT PRATICAL, BUT THE SIPHON IS FOR NOW OUR STEAM TRAP!

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