The working condition of pulverized coal pipeline is really bad. The temperature is high, the flow rate is fast, and the pulverized coal particles grind the tube wall like sandpaper. Ordinary expansion joints are installed, and if you are lucky, it will last for half a year. If you are unlucky, you will perforate and leak powder for three months. You calculate the cost of shutdown and replacement once, labor plus spare parts plus shutdown loss, enough to buy several serious goods.
Two days ago, I met a power plant customer, who complained to me that the general-purpose corrugated expansion joint they used before was worn out in less than half a year, and the bellows was directly eroded out of small holes, and pulverized coal was sprayed everywhere. Tsk, this is not saving money, it is simply burning money. Then what kind of expansion joint can withstand the destruction of pulverized coal pipeline?
The 'killer' of pulverized coal pipeline: wear, high temperature and erosion
In pulverized coal conveying pipeline, the wind speed can usually reach 20-30m/s, and the impact force of particles hitting the inner wall plus continuous friction is the typical erosion wear. Moreover, the temperature of pulverized coal is not low, and the pulverizing system is basically 80-120℃, and the temperature in the outlet area of coal mill is higher. Ordinary carbon steel bellows In this environment, the surface oxide scale peels off quickly, and then the parent metal is directly exposed, which accelerates corrosion and wear.
More fatally, pulverized coal pipelines usually have vibration, and installation deviations are inevitable. The expansion joint has to absorb both thermal displacement and axial and transverse loads. The wall thickness of ordinary bellows is only 0.8-1.2mm, which can't be carried at all-just like asking a thin man to do the work of moving bricks, and it's weird not to get down.
Structural Hardcore Upgrades: Deflectors, Thick-walled Bellows and Wear-Resistant Liners
To solve this problem, the metal bellows expansion joint for pulverized coal has to be hardcore upgraded in design. First of all,guide tubeThis thing isn't just a sleeve. It is inside the expansion joint, guiding the airflow through smoothly, avoiding the coal powder directly washing the trough of the bellows. In this product, the specific function of the expansion joint guide tube is to protect the bellows and reduce the secondary wear caused by vortex. The thickness of the guide tube must be thickened, for example, 6mm or even 8mm wear-resistant steel, and the surface must be heat-treated and hardened.
Secondly,Thick-walled bellows。 The wall thickness of ordinary expansion joint bellows is about 1mm. It is recommended to choose 304 or 316L stainless steel with at least 1.5-2mm under pulverized coal condition. Don't underestimate the increase of a few tenths of millimeters, and the fatigue life can be doubled several times. Of course, it is difficult to form a thick wall, which is why many factories can't do it-their equipment pressure is not enough.
The third line of defense isWear-resistant liner。 Some manufacturers will use tortoise shell mesh lining ceramic or lining wear-resistant cast stone.Large diameter thick wall expansion jointThis scheme is often used. The inner lining isolates the pulverized coal particles on the wear-resistant layer, and the bellows body is almost immune to impact. With this set of combined punches, the lifespan was stretched from half a year to more than two years, which was not difficult.
How is it different from expansion joints used in power stations and cement industries?
What is the difference between corrugated expansion joints used in power station industry and metal corrugated expansion joints used in cement industry and those used in pulverized coal?
The working conditions have different emphases. Power station pipelines are mainly steam and flue gas, with high temperature and high pressure, but the medium is relatively clean, with emphasis on high temperature resistance and fatigue. Cement industry pipelines are filled with raw powder and clinker dust, and the particles are coarser and harder than pulverized coal, but the temperature is usually lower. The pulverized coal pipeline is the superposition of high-speed solid-containing air flow + medium temperature + vibration, which tests the erosion wear resistance and stable compensation ability.
Therefore, for the expansion joint used in pulverized coal, the guide tube must be thicker, the lining must be more wear-resistant, and the wall thickness of the bellows must also be higher than that used in the cement industry. In addition, the strength requirement of the tie rod is also higher-because the self-weight of pulverized coal pipeline is often greater, the tie rod has to bear more blind plate force. This site'sLarge tie rod expansion jointIt is often selected in pulverized coal projects, with better rigidity and strong deviation adjustment ability.
Installation Pit Avoidance Guide: How to Adjust the Tie Rod? Don't reverse the direction of the guide tube
If you choose the right equipment, if the installation rolls over, it will still be useless. Let's startDirection of guide tube-The expansion joint is generally marked by an arrow, and the arrow must point to the flow direction of the medium. Arrow is not accurate? The opening of the guide tube is reversed, and the pulverized coal is directly poured into the gap of the bellows, which will wear out in a few days. Before, a customer installed it backwards, and came to complain that the product was not good. We sent someone to take a look, and the arrow was clearly marked, but he didn't look at it himself. Alas, this wrongful money is really not worth it.
Againtie rod nut adjustment。 The tie rod nut is usually locked before installation, this is to protect the bellows from being stretched or compressed during transportation and hoisting. After the pipeline is in place and the flange bolts are tightened, the tie rod nut must be loosened to the pre-compression amount required by the design. How exactly to adjust? Confirm the cold displacement direction of the pipeline first, and then adjust the nut position accordingly. Generally speaking, there should be a 1-2mm gap between the tie rod nut and the ear plate to ensure the expansion and energy saving free expansion and contraction. After adjustment, you have to confirm that all nuts are not loose-there are detailed steps in the question and answer on how to adjust the expansion joint tie rod nut in this site, which can be done comparatively.
Does the screw of the expansion joint need to be removed?After installation, do not remove the tie rod bolt, it is used to limit the excessive deformation of the bellows. If the bolts are completely removed, the bellows may be broken by the pipe's own weight, or excessive tension under pressure may lead to instability. Only adjust the nut position, the screw remains.
Real case: The life of a power plant was extended from half a year to two years after replacement
Finally, let's talk about a real case. A batch of ordinary single axial expansion joints were used in the pulverized coal pipeline of the pulverizing system of Unit 4 in a power plant in Hebei Province. After 6 months of operation, the powder began to leak, and it took more than a year to shut down the machine for repair welding. Later, he asked us to make a plan and replaced it withExpansion joint of metal bellows for pulverized coalThe structure is thick-walled bellows + thickened guide tube + lined with tortoise shell mesh ceramic.
During the installation, we guided the adjustment of the tie rod on the spot, and the direction of the guide tube was checked one by one. It has been almost two years since it was put into operation. Every year, the furnace is shut down for maintenance and inspection. The wear of the guide tube is only 30%, and the bellows is intact. The customer calculated an account: the expansion joint was changed twice a year before, with more than 40,000 spare parts and labor each time, plus 200,000 shutdown losses per day. Now I haven't changed it for two years, and the money saved is enough to buy several sets.
So you say that choosing the right expansion joint is essentially saving yourself trouble. In this heavy wear scene of pulverized coal pipeline, don't make do with general goods. Targeted design is really cost-effective.