Let's talk about what the deflector does first-what's the difference between it and the deflector?
Flue expansion joint deflector, to put it bluntly, is a layer of metal "armor" welded inside the expansion joint. You may ask: Is it the same thing as a guide tube? Really not. The guide tube is usually a complete inner sleeve with fixed ends, and its main function is to guide the flow direction of the medium and reduce the vortex; The deflectors, however, are often arranged in sections and fixed near the crest or trough of the expansion joint, more like a row of "baffles". For an intuitive example: the deflector is like a liner in a pipe, and the deflector is like a shield. InMetal rectangular expansion jointOrAmong the corrugated expansion joints used in power stations, the most common goal of the deflector is one-to block the high-speed flue gas and prevent it from directly washing the bellows wall.
Can you remove that deflector? I said if you want to change the expansion joint every three months, then remove it. He immediately fell silent.
The temperature in the flue is high and the dust is large. How can the deflector protect the expansion joint from being washed away?
How hard is the flue working condition? The flue gas temperature is always above 400℃, the dust concentration can reach tens of grams per standard cubic meter, and the particle speed is tens of meters per second. If the bellows were directly exposed to this airflow, it would be sanding the steel plate — it would not take long to wear out. The function of the deflector is to "block the gun": it guides the mainstream smoke away from the corrugated surface, allowing the airflow to walk against the deflector, and the corrugated area only bears the swirling flow with lower flow velocity. CooperateNon-metallic expansion jointThe thermal insulation layer in the bellows can also reduce the direct heating of the bellows by thermal radiation. In practical cases, the service life of the expansion joint with the deflector can be prolonged by 2~3 times or even higher. Do you think this thing is worth it?
However, note that the deflector is not just soldered with iron sheets. It must match the displacement direction of the expansion joint-for example, for an axial expansion joint, the deflector must leave enough clearance, otherwise it will die when compressed, and instead pull the bellows out. The thickness, material and fixing method of the deflector are all particular. If you make a mistake, you will dig a hole for yourself.
What is the difference in design between deflectors used in power stations and cement plants?
Generally, the flue of power station operates under negative pressure, and the flue gas temperature is high but the dust is relatively uniform; In cement factories, the waste gas at the end of the kiln has high dust concentration, coarse particles and alkaline substances. Therefore, the deflector used in power stations is usually made of 304 or 316L, with a thickness of 4~6mm, and is welded at the trough position; Cement plants have to use thicker wear-resistant steel plates (such as 16Mn or even NM400), and the surface of the deflector should be hardened or welded with wear-resistant layers. InIn the metal corrugated expansion joint of the cement industry, the deflector often has to consider preventing dust accumulation-designed at a certain inclination angle to let the dust slide down, instead of piling up in the corrugated folds.
Another exampleFor the expansion joint behind the desulfurization flue gas baffle door, the flue gas has high moisture content and acid corrosion, so the deflector must be lined with PTFE or duplex stainless steel. For the same part, when the working conditions change, the design ideas are very different. If you take the scheme of the power station directly to the cement plant, it's weird that it's not bad.
How to match deflectors with smoke baffle doors and non-metallic expansion joints so as not to fight?
In many systems, next to the expansion jointFlue gas baffle doors (such as double-sealed single-axis round baffle doors or single-axis double baffle doors). When the baffle door opens and closes, the direction of the airflow changes abruptly, and if there is no deflector, the impact acts directly on the expansion joint. What to do? Install a deflector on the outlet side of the baffle door to let the airflow run smoothly and then enter the expansion joint. Likewise,Non-metallic expansion joints usually have fabric layers and heat insulation cotton inside, and the deflector must avoid these flexible materials, so it can't be directly welded to the frame. Generally, a lining steel ring is made first, and then the deflector is fixed on the steel ring. encounterFor rectangular non-metallic expansion joints, the deflector must also match the position of flange bolt holes to avoid interference with the sealing surface.
To put it bluntly, the deflector is a "lubricant"-let the baffle door, expansion joint and pipe work together, not compete with each other.
The easiest points to overlook when selecting deflectors, you will understand if you step on too many pits
First, many people only care about the deflector material and ignore the fixing method. The weld is not strong enough, it falls off after a few months of operation, and then it is swept into the expansion joint by the airflow, scratching the bellows to pieces. It is recommended to use continuous full welding, not spot welding.
Second, the length and clearance of the deflector. Too short will not stop the airflow, and too long will affect the displacement of the expansion joint. Usually, the length of the deflector extending into the pipe should cover 60% ~70% of the total length of the expansion joint, leaving a gap of 10~15mm with the opposite pipe wall. I have adjusted countless devices with this data, and it is easy to have problems if the deviation is greater than 5mm.
Third, the "direction arrows" of the deflectors are not blindly marked.The direction of the arrow of the expansion joint generally points to the direction of the media flow, but the bevel of the deflector must be oriented in the opposite direction-allowing the media to hit the back of the deflector first to create a buffer. Many installers don't know this detail, and installing it backwards will aggravate the scouring.
Fourth, followWhen the electric plug-in plate type insulation door is matched, the deflector plate cannot block the movement track of the plug-in plate. Once on-site debugging, the plug-in board was stuck by the deflector as soon as it was turned off, and finally it had to be cut off and re-welded. In the design stage, three-dimensional simulation is required, not empirical estimation.
I've stepped on these pits, so you don't have to step on them again. Choosing the deflector is a small part in the smaller case, but in the larger case, it is related to the reliability of the whole flue system. Next time, when you encounter the selection of flue expansion joint deflector, don't just look at the price, ask more about the structural details-you know whether it's worth it or not.