Technical Illustration of Condensate Formation

Transcription

1 Condensate Recovery As hot steam cools down inside a mill s pipes, the droplets of vapor turn into condensate water. If recycled, this condensate water can provide mills with an inexpensive source of clean water and heat energy that would otherwise be lost. While nearly all mills collect and recycle condensate water to some extent, very few do it correctly. Most mills only recover and reuse around thirty percent of their condensate, while allowing the rest to go to waste. In this module, we will review various Clean By Design best practices that will help your mill to recover and reuse condensate much more efficiently and completely. 1

2 Technical Illustration of Condensate Formation As hot steam cools down inside a mill s pipes, the droplets of vapor turn into condensate water. If recycled, this condensate water can provide mills with an inexpensive source of clean water and heat energy that would otherwise be lost. 2

3 Most Mills Recover Only 30% of Condensate While nearly all mills collect and recycle condensate water to some extent, very few do it correctly. Most mills only recover and reuse around thirty percent of their condensate, while allowing the rest to go to waste. 3

4 Objectives By the end of this module, you should be able to Identify potential sources and estimate available quantities of recoverable condensate water Identify processes where recovered condensate water can be applied Summarize the general principles for mapping the pipe structure of a condensate recovery system In this module, we will review various Clean By Design best practices that will help your mill to recover and reuse condensate much more efficiently and completely. By the end of this module, you should be able to Identify potential sources and estimate available quantities of recoverable condensate water Identify processes where recovered condensate water can be applied Summarize the general principles for mapping the pipe structure of a condensate recovery system 4

5 Objectives By the end of this module, you should be able to List and describe various power sources for a condensate recovery system and the advantages and disadvantages of each Explain how discharging condensate water prevents serious problems such as water hammer and pipe erosion Calculate the cost savings for your mill from recovering and reusing condensate water List and describe various power sources for a condensate recovery system and the advantages and disadvantages of each Explain how discharging condensate water prevents serious problems such as water hammer and pipe erosion Calculate the cost savings for your mill from recovering and reusing condensate water 5

6 Recovery Why Mills Should Recover Condensate 6

7 Technical Illustration/Simple Animation of Condensate Formation When hot steam comes into contact with a cooler object - such as product, pipes or equipment - heat energy from the steam is transferred to the object, causing its temperature to increase, Meanwhile as the steam loses energy, a portion of the water vapor in the steam will turn back into liquid water. Water that forms when steam loses heat energy is called condensate. 7

8 Recovering Condensate Specific enthalpy (kj/kg) Total energy in steam Total energy in condensate Pressure bar g In a perfectly efficient mill, the ratio of steam to condensate would be even: in other words, if the mill produced one kilogram of steam per hour of operation, then - eventually - one kilogram of condensate water per hour would need to be discharged from the pipes and equipment. However, in reality, the ratio of condensate to steam is typically between thirty to sixty percent. Condensate water is usually very clean, making it excellent for reuse in production. It also contains a significant amount of heat energy - typically anywhere from twenty to thirty percent of the heat originally contained in the steam. When we allow this condensate to go to waste, it adds up to a significant loss of water and energy. 8

9 Ideally, image of recovered water being fed into boiler Fortunately, both the water and heat contained in condensate can be recovered and reused in a variety of ways throughout the manufacturing process. For instance, recovered condensate can be fed back into the boiler s deaerator. 9

10 Another image of recovered water being fed into boiler This is much more efficient than replenishing the boiler with fresh water: Because the temperature of the condensate is already quite high, it takes less energy to bring it up to steam temperature. And because condensate is free of pollutants and minerals, it can be returned directly to the boiler without requiring treatment. 10

11 Boiler Efficiency Increased by 10-20% Boiler Image Feeding a boiler with recovered condensate can improve the boiler s output capacity by ten to twenty percent, while reducing fuel consumption by three to ten percent. 11

12 Waste-Heat Boilers Increased capacity % This is especially important for a waste-heat boiler, which produces recoverable, low pressure steam from the boiler s flue gas. Facilities that use condensate water instead of fresh water can increase the capacity of their waste-heat boilers by fifty to a hundred percent. 12

13 Reducing Emissions Carbon Dioxide Nitrogen Oxide Sulfur Oxide By reusing condensate water in its boiler, a mill can save money and fuel, as well as reduce emissions of pollutants like carbon dioxide, nitrogen oxide and sulfur oxide, improving the mill s overall carbon footprint. 13

14 Uses for Hot Condensate Energy Source Hot Water Source Water for Dyeing Steam (Reused Flash Steam) Feeding condensate water back into the boiler is just one way that condensate can be re-used. Hot condensate can also be used: As a source of energy for various heating systems As a source of clean, hot water for washing equipment As hot, clean, soft water for dyeing And As steam, by reusing the flash steam that is created when hot water crosses from a high-pressure area of the system to a low-pressure area. 14

15 Image of workers near pipes Condensate water recovery can also be a safety issue. When condensate in steam pipes is subjected to pressure, it can damage the pipes and cause leakage - or, in extreme cases, even cause violent explosions that endanger workers. By recovering condensate before it builds up, we can prevent these hazards. 15

16 Case Studies REAL-WORLD EXAMPLES 16

17 Interview Subject Position, Name of Plant Location of Plant In 2014, a mill in Shaoxing participating in the Clean By Design program was able to reclaim five percent of its total steam consumption by implementing a steam condensate water recovery system. Before the system was implemented, the mill s condensate water would go directly to the wastewater drain. Even though they knew that condensate water was potentially valuable, the managers at the mill did not try to recover it, as they thought there wasn t enough condensate to make the effort worthwhile. After some research, the mill invested one hundred thousand renminbi on a pilot project to test recovering condensate water. They discovered that they were able to recover and reuse thirty percent of the mill s steam energy, and that the condensate water provided a significant source of industrial water as well. 17

18 Sources & Applications SOURCES OF AND USES FOR CONDENSATE 18

19 Sources of Condensate Identify areas where condensate occurs Determine how much is being produced Measure amount already being collected Measure temperature Clearly, there are significant benefits to recovering condensate water. But before we can implement a recovery system, we need to Identify areas where condensate occurs: Determine how much condensate is being produced; Measure how much condensate, if any, is already being collected; And Measure the temperature of the condensate, as this might affect how and where we reuse it. 19

20 Sources of Condensate Washing Machines Dyeing Vats Drying Cylinders Ageing Machines Setting Machines In dyeing and printing mills, condensate will most commonly occur around: Washing machines Dyeing vats Dry cylinders Ageing machines and Setting machines 20

21 Determining Volume Container with Markings Volume of Condensate = Volume of Steam When used directly, collect in container with markings To determine the volume of discharged condensate water, you can use one of two simple methods: First: in cases where steam is used as source of indirect heat, the volume of condensate water will be equal to the volume of indirect steam. And second: In cases where condensate is reused directly, simply collect the condensate water in a container with markings to indicate volume. 21

22 Calculating Savings Download zip file with spreadsheet tool Instructions Download Refer to the section in the course workbook on XX, which provides a form to help you identify and quantify sources of condensate water in your mill. 22

23 Setting Goals for Reuse 80% 30% Once you know how much condensate water is being generated within your mill, you can begin to set goals for condensate recovery and reuse. As stated before, most mills recover only thirty percent of their condensate water. However, by implementing a few simple best practices, most mills can recover eighty percent or more of their condensate. While you are free to set your own targets, Clean By Design recommends eighty percent as a reasonable goal for most mills. 23

24 Setting Goals for Reuse Key Statistics Amount of condensate produced in a typical year Current recovery and reuse rate Potential energy, water and economic savings from implementing different condensate recovery measures To help you with planning, Clean By Design has developed tools for estimating key statistics such as: The amount of condensate water that your mill produces in a typical year The current recovery and reuse rate And The potential energy, water and economic savings from implementing different condensate recovery measures Let s look at how to use these tools more closely. 24

25 Interactive Example Here s a real-world example of how these tools can be practically applied. [Provide an example (e.g. Mill A) that follows the estimation steps.] Based on your findings, you can prioritize the implementation of different condensate recovery measures according to your schedule and budget. 25

26 Uses for Condensate Boiler Feed Water Images Dyeing Rinsing Washing Heat Transfer Once we know how much condensate will be recovered, the next question is, How can we use the reclaimed water and energy within our mill? The most efficient use of condensate is to return it directly to the boiler feed water tank to produce steam. Other common applications include processes such as dyeing, rinsing and washing. A slightly less efficient way to reuse condensate is to indirectly transfer heat from the condensate water to the inlet fresh water used for dyeing, rinsing or washing. Some mills have found other, innovative uses for condensate, such as using it as a source of thermal power for air-conditioning units. 26

27 Pipe System Pipe Layout and Steam Traps 27

28 Steam Traps Pipes Power Source After you have identified the most promising sources and uses of recovered condensate water, the next step is to develop a plan for collecting and transporting condensate from its source to the destination. There are three main components of a condensate recovery system: Pipes to transport the collected condensate Steam traps to collect condensate And A power source - such as gravity, inlet pressure or a pump - to move the condensate from its source to the destination We will discuss steam traps in detail in another module. For now, we will focus on the other to parts of the system: pipes and power sources. 28

29 In situations where condensate water will be collected from one process then reused in a different process, you will need to install pipes to transport the condensate. Steam systems in mills are very complicated, and determining the best way to recover and transport condensate water within your mill will require careful analysis by a highly-trained engineer. However, there are some general principles for mapping out a pipe structure for a condensate recovery system that will apply in nearly all situations. 29

30 Pipe Layout Key Factors The diameter of the pipe The length of the pipe The pipe route The key factors to consider are: The diameter of the pipe The length of the pipe And The pipe route 30

31 Simple technical illustration / animation of condensate flow within pipe First, let s discuss pipe diameter. To determine an appropriate diameter for condensate recovery pipes, we need to consider the amount of flash steam and condensate that might be present in the pipes, as well as the pressure and flow velocity. Too often, mills make the mistake of sizing condensate recovery pipes based on the average rate of condensate flow. This can cause problems in situations where flow velocity is variable, and sometimes reaches levels much higher than the calculated average. To calculate the most appropriate pipe diameter, we need to estimate the volume ratios of both condensate and steam at a given pressure, then determine a maximum allowable flow velocity. 31

32 Other Factors Live Steam Corrosion Image of corroded pipe Mud Consult a professional engineer for recommendations Mills also need to account for the presence of live steam and the long-term buildup of corrosion and mud. Both of these can increase flow velocity, pressure drop, and system backpressure. During the planning phase, you should have a professional engineer inspect the condition of your pipes and make recommendations to account for these factors. 32

33 Calculating Savings Download zip file with spreadsheet tool Instructions Download The engineers at Clean By Design developed a tool to help you determine an appropriate pipe diameter for your mill, which can be found on the [] tab of your [workbook] However, this tool should be used only for estimation. Before developing a plans, you should consult with an expert to make sure that any other factors specific to your mill have been accounted for 33

34 Simple technical illustration showing pipe route, downward slope Now, let s take a look at pipe length and route. When determining the length and route of condensate recovery pipes, the goal is to minimize pressure resistance and keep the overall pipe length as short as possible. That means that a well-designed recovery system will allow condensate to move mostly downward, to take advantage of gravity, and have as few bends in the pipe route as possible. 34

35 Pipe Layout To ensure that heat energy is not lost as the condensate flows through the pipe system Re-use the condensate as close to the point of recovery as possible Keep condensate water pipes wellinsulated to maintain a temperature above 90 C Use separate pipes for cool and hot water To ensure that heat energy is not lost as the condensate flows through the pipe system, you ll want to take the following actions: Re-use the condensate as close to the point of recovery as possible; Keep condensate water pipes well-insulated to maintain a temperature above ninety degrees celsius; And Use separate pipes for cool and hot water. 35

36 Power Sources Powering the Recovery System 36

37 Once we have mapped our pipe structure, we will need to add a power source to balance the pressure within the pipes and keep the system operating smoothly. 37

38 Simple animation showing balance of pressure The pressure inside condensate pipes must be balanced in order to keep the condensate water moving towards its intended destination, such as a condensate collection area or return header. Malfunctioning steam traps, long pipe routes and changes in elevation can create pressure problems in a condensate recovery system. Meanwhile, long vertical and horizontal distances can increase system backpressure. These factors can slow, block or misdirect the flow of recovered condensate within the system. There are two power sources that mills commonly use to overcome condensate return or backpressure: trap inlet pressure and pump pressure. Let s take a look at each.. 38

39 Inlet Pressure Normally, even if the backpressure is not very high, inlet condensate water has enough residual positive pressure to send the water to its destination. Relying on inlet pressure to transport condensate is typically the lowest-cost and most reliable option, as it requires no special equipment and little effort to implement. Whenever possible, it should be our first choice for powering the system. There are two ways to configure condensate recovery systems to utilize trap inlet pressure: Transport piping and steam traps can be set up to let condensation drain downward to its destination. This installation makes use of residual pressure and gravity to carry the water to the final vessel or reuse location. Some steam traps in the system have a much higher residual pressure than others. These higher-pressure steam traps can create negative pressure on lower-pressure steam traps, disrupting the discharge of condensate water. One way to overcome this is by having the high-pressure traps discharge upward, via an elevated return. It s a viable solution so long as the differential pressure remains positive and appropriate site safety standards are followed. 39

40 Return to simple animation showing balance of pressure Sometimes, the residual pressure of steam traps is simply not enough to overcome backpressure and successfully transport condensate water through the pipes. In these situations, a pumping system can be installed to balance pressure and propel the water to its destination. 40

41 Pumping Systems 3 Main Sources of System Backpressure Lift after a steam trap Frictional loss of transport piping Static pressure associated with the destination recovery vessel To calculate the amount of pressure that a pump must generate, we need to start by estimating the system backpressure. This can be calculated by finding the sum of the backpressure forces, or Total Dynamic Head. The three main sources of system backpressure are: Lift after a steam trap Frictional loss of transport piping and Static pressure associated with the destination recovery vessel Again, you should consult a professional engineer to assess the amount of backpressure present in your mill s steam system and set an appropriate pressure level for your pump. 41

42 Electric Pumps Pumps can be powered by electricity, steam or air. However, electricallypowered centrifugal or turbine condensate pumps are the most popular options for condensate recovery systems. They make it easy and inexpensive to increase delivery pressure and obtain a positive pressure differential. Typically, condensate water would be collected in a tank and then electricallypumped to reuse locations. This lets us recover and transport condensate across much greater distances and elevation changes than would be possible using trap inlet pressure alone. 42

43 Cavitation You should now be able to Installing specialized centrifugal pumps that do not experience cavitation Installing an elevated collection tank (or collecting header) Using steam pressure to increase the pressure within the tank, provided the components can handle the increased pressure and heat Condensate is a valuable source of clean water and heat energy that your mill can use in a variety of ways. By taking measures to improve recovery of condensate, your mill can enjoy significant energy and resource savings for years to come. Having completed this module, you should now be able to Identify potential sources and estimate available quantities of recoverable condensate water Identify processes where recovered condensate water can be applied Summarize the general principles for mapping the pipe structure of a condensate recovery system 43

44 Mechanical Pumps An alternative to electric pumps is using a mechanical pump powered by compressed air or steam. Mechanical condensate pumps that rely on positive displacement, as opposed to impeller rotation, eliminate the danger of cavitation, making them increasingly popular among mills. Given that they don t require electricity, these pumps are also well-suited for remote locations and environments with a high risk for explosions. In recent years, the variety and capacity of mechanical pumps have improved considerably, making them an increasingly popular choice for condensate recovery systems. 44

45 Common Issues Water Hammer, Erosion and Water Strike 45

46 Condensate Under Pressure Water Hammer Pipe Erosion Recovering condensate water from pipes isn t just a matter of conserving resources: failure to discharge condensate water from pipes can lead to serious problems and safety hazards. As water and steam move through pipes, the pressure created can damage the pipes in a variety of ways. Two common problems related to pressure are water hammer (or vibrations resulting from sudden changes in pressure within steam pipes) and pipe erosion. 46

47 Water Hammer Anyone who has worked in a factory with steam pipes will be familiar with the repetitive, metallic banging noise known as water hammer. Water hammer occurs when steam moves rapidly through pipes and causes the condensate water inside the pipes to vibrate and ripple, like a strong wind creating waves in the ocean. Occasionally, water hammer will produce a violent boom followed by loud vibrations. 47

48 Water Hammer Can Damage Junction Gaskets Valve Flanges Valves Sensors The vibrations from water hammer can severely damage the piping system, particularly junction gaskets, valve flanges and valves. Steam or hot condensate blowing out of damaged junctions can lead to serious accidents and pose a safety hazard to workers. Water hammer can also damage sensors, causing inaccurate meter readings. 48

49 Water Hammer Common solutions for water hammer Ensuring pockets of steam remain small Avoid or discharge steam Use different lines for water of varying temperatures Avoid contact between hightemperature steam, low-temperature condensate While water hammer is mostly associated with steam pipes, it can be an even bigger problem in condensate water pipes, as there is more water present. In most cases, water hammer can be reduced or eliminated by applying some very simple solutions - though for complicated situations, you should seek the advice of an expert. Common solutions for water hammer include: Ensuring that pockets of steam remain small; Avoiding or discharging the steam (for instance, flash steam) that is causing the problem; Using different lines for water sources of varying temperatures; And Wherever possible, avoiding contact between horizontal pipe segments of high-temperature steam and low-temperature condensate. 49

50 When this happens, a chugging noise will be heard as the high-temperature steam cools down. While the force generated is not great, the resulting noise can become a problem, as previously mentioned. If avoiding contact between the hot steam and lower-temperature condensate is not possible, then using a small pocket is a good option to reduce the problem. 49

51 Pipe Erosion Under pressure, condensate water moving through a pipe system can act like an industrial water jet, cutting and wearing away the walls of carbon-steel pipes. This is a major cause of steam pipe leakage in most mills. And pipes installed exclusively for condensate water recovery contain much more water than steam pipes, putting them at greater risk for erosion. 50

52 Pipe Erosion To prevent pipe erosion Eliminate direction changes when possible Locate traps upstream, away from direction changes Use oversized discharge pipes when cost-effective Select steam traps with continuous (not intermittent) flow Avoid bucket, disc, piston, thermostatic traps Here are some actions you can take to help prevent pipe erosion: Eliminate direction changes when possible; Locate traps upstream and away from direction changes; Use oversized discharge pipes when it is cost effective; and Select steam traps with a continuous, rather than intermittent flow. Specifically, avoiding bucket, disc, piston, and thermostatic traps if possible. We will learn more about these various kinds of steam traps later in this series. 51

53 Evaluation Calculating the Benefits Part V. Calculating the Benefits of Condensate Recovery and Reuse 52

54 Calculating Savings Download zip file with spreadsheet tool Instructions Download To calculate the benefits from condensate recovery, we can refer to the same tool that we used to initially prioritize condensate recovery projects. After implementing your solutions and collecting a sufficient amount of data, run the calculations again to determine the cost and resource savings. 53

55 Evaluating Condensate Recovery Measures 1 2 Have we achieved our goals for recovering condensate water? Clean By Design recommends a goal of recovering 80% or more of condensate water produced Is the temperature of the condensate collected higher than Ti0? Yes No further measures are required beyond routine maintenance according to schedule No Revisit plans and implement new or different measures for successful condensate recovery Once we have implemented condensate recovery measures, there are two main questions to ask when determining whether or not the measures have been successful. First - have we achieved our goals for recovering condensate water? Again, Clean By Design recommends that mills try to recover eighty percent or more of their condensate water. If we have reached our target, then no further steps are needed. If not, then we need to calculate the difference between the target and our actual recovery and reuse rate. If the difference is greater than ten percent, it may be necessary revisit our plans and implement new or different measures for condensate recovery. If the difference is less than ten percent, then it could be possible to close the gap through minor adjustments and improvements to existing measures. The second major question is whether the temperature of the condensate collected is higher than Ti0. 54

56 If it is, then no further measures are required beyond performing routine system maintenance according to schedule. However, if the temperature falls below TI0, then we need to revisit our plans and implement new or different measures to ensure that more heat energy is successfully reclaimed from condensate water. 54

57 Conculsion SUMMARY OF OBJECTIVES 55

58 Recap of Objectives You should now be able to Identify potential sources and estimate available quantities of recoverable condensate water Identify processes where recovered condensate water can be applied Compare centralized vs. onsite wastewater heat recovery systems Condensate is a valuable source of clean water and heat energy that your mill can use in a variety of ways. By taking measures to improve recovery of condensate, your mill can enjoy significant energy and resource savings for years to come. Having completed this module, you should now be able to Identify potential sources and estimate available quantities of recoverable condensate water Identify processes where recovered condensate water can be applied Summarize the general principles for mapping the pipe structure of a condensate recovery system 56

59 Recap of Objectives You should now be able to List and describe various power sources for a condensate recovery system and the advantages and disadvantages of each Explain how discharging condensate water prevents serious problems such as water hammer and pipe erosion Compare centralized vs. onsite wastewater heat recovery systems List and describe various power sources for a condensate recovery system and the advantages and disadvantages of each Explain how discharging condensate water prevents serious problems such as water hammer and pipe erosion Calculate the cost savings for your mill from recovering and reusing condensate water 57

60 Module Complete ADVANCE TO THE NEXT MODULE WHEN READY Advance to the next module when you are ready to continue. 58