Too much resistance to boiler flue expansion joint? Three-step selection method helps you save fan electricity bill
Two days ago, I met a friend from a power plant. As soon as I came up, I complained: three or four kinds of flue expansion joints have been changed, and the fan current is still frighteningly high, and the electricity bill costs tens of thousands more a month. Do you think this is irritating? Actually,Boiler flue expansion joint resistanceIt's not as mysterious as you think at all. Many problems are the mines buried during the selection or installation. Today, let's break it up and have a chat, and get it done in three steps. To ensure that you finish it according to it, the energy consumption of the fan will be reduced by at least 20%.
Step 1: Find out exactly where the resistance comes from-the self-inspection list of the internal structure of the expansion joint
Don't blame the expansion joint itself as soon as it comes up. You first take a flashlight and open the flue to see what is going on inside. I'll make a self-test list, and you check them one by one:
- Is the deflector crooked?The function of the guide tube is to guide the flue gas to pass smoothly. If it is deviated, deformed or too short in length, the flue gas will collide inside the expansion joint, forming a vortex. Can the resistance not be great?
- Is there any dust accumulation between the ripples?Especially for metal corrugated expansion joints, if the dust accumulation in the peaks and valleys exceeds 2cm thick, the flow section will directly shrink and the resistance will double.
- Is the skin of the non-metal expansion joint bulging?When the fabric fiber expansion joint is used for a long time, the interlayer peel off or the inner fabric collapses, which will also cause local throttling.
- Is the tie rod nut locked?Some installers try to save trouble and screw the tie rod nut to death, and the expansion joint can't expand and contract freely, which is equal to hard carrying, and it is strange that the resistance doesn't soar.
This self-examination will take you less than half an hour, but it will help you eliminate 70 to 80 percent of low-level problems. If you find the above situations, don't rush to replace them, repair them and adjust them, and the resistance will drop immediately.
Step 2: Judge whether you should use metal corrugated expansion joint or non-metal expansion joint (with resistance calculation formula)
Okay, the self-examination is over, and the problem is still there. That's when we have to re-select. Many people struggle: in the end, useMetal corrugated expansion jointStillNon-metallic expansion joint (fabric fiber expansion joint)？ Let me tell you a practical guideline-look at the temperature and pressure of the medium.
- The flue gas temperature exceeds 400℃, or the pressure is greater than 0.1MPa? Honestly choose metal, likeHigh temperature axial expansion jointOrUniversal corrugated expansion joint。
- The temperature is not high (Non-metallic expansion jointIs the first choice, its corrugation is soft and resistance is inherently less than that of metal.
But! It's not enough to choose the right type, but if the size is wrong, you will still step on the pit. Give you a formula for resistance calculation, remember:
"The diameter of the pipe should be large rather than small, the wave number should be less than more, and the inner diameter of the guide tube should be flush."
What's the meaning? The nominal diameter of the expansion joint is preferably 10-20mm larger than the actual inner diameter of the flue to avoid necking; As long as the number of ripples is enough, don't add a few more waves for good looks. Every extra wave of resistance will go up a section; The inner diameter of the guide tube must be flush with the inner wall of the flue. If the height difference exceeds 5mm, wait for the fan to be overloaded.
The inner diameter of your flue is 800mm, selectMetal rectangular expansion jointWhen, the diameter is recommended to be above 820mm. Don't feel bad about that little material money. The fan electricity bill saves much more than the expensive one.
Step 3: Change these four details during installation, and the resistance can be reduced by 20%
If you choose the right expansion joint, it will be too unfair to install it again. The following four details, you spend half a day rectifying them, the effect is immediate:
- Guide tube orientation: The direction of the arrow of the guide tube must be consistent with the direction of flue gas flow. Just wait for dust to block it. There was a cement factory beforeMetal Corrugated Expansion Joints in Cement IndustryThe deflector was installed backwards, and the resistance tripled.
- Pre-stretching amount of tie rod: When installing the metal corrugated expansion joint, adjust the tie rod nut according to the cold tightness of the pipeline. Too much or too little pre-stretching will cause abnormal stress and increase resistance. Look at the design drawings for specific values, don't screw them by feeling.
- Connection mode of expansion joint and flue: Try to use welding and less flange connection. When the flange gasket is thick, it will protrude into the inside of the flue, forming a step. If you have to use a flange, userubber compensatorOrRubber PTFE compensatorThe inner diameter of the gasket should be consistent with the inner diameter of the pipe.
- Length of straight pipe section before and after expansion joint: Leave at least 2 times the straight pipe section in front of the expansion joint and 1 time in the back. If it is short, the flow pattern of smoke will be turbulent and the resistance will rise.
Tsk, many manufacturers don't care about these at all when installing them. After installing them, they pat their butts and leave. As the owner, you keep an eye on them to make changes, and then check and accept them after making changes. After all these changes, the resistance dropped by 20% is really not blowing.
Attachment: Troubleshooting table for abnormal resistance of common boiler flue expansion joint (just follow the measurement)
Finally, I will give you a checklist, which lists the common problems, causes and solutions clearly. You print it out and post it in the control room, and the operator can check it every day when he inspects it.
| Phenomenon | Probable cause | Screening Methods | Solution |
|---|---|---|---|
| The fan current continues to be on the high side without fluctuation | Small diameter of expansion joint or necking of guide tube | Measure the pressure difference before and after the expansion joint, if it exceeds 100Pa, it is suspicious | Replaced withLarge diameter thick wall expansion jointOr add expanded diameter section |
| Periodic fluctuation of current | Dust accumulation in corrugation or skin bulging | Use an endoscope to see the internal dust accumulation | Cleaning or replacingNon-metallic expansion jointFabric layer of |
| The vibration at the expansion joint of one platform is obvious | Pull rod locked or improperly preloaded | Check that tie rod nut is loose/too tight | Readjust the tie rod according to instructions |
| Flue wall temperature abnormal near expansion joint | Dropping or displacement of guide tube | Visually inspect guide tube position after shutdown | Re-weld or replace deflector |
| The wind turbine current suddenly soared without warning | Foreign body blockage inside expansion joint | Check the expansion joint inlet for debris | Clean up and reinstallFlue gas baffle doorFiltration |
Okay, that's all. You follow these three steps,Boiler flue expansion joint resistanceNine times out of ten, the problem can be solved. If you still can't get it done, it may be the design of the whole flue. Talk to me then.