What inspiration can be given to the spiral finned tubes for the Economizer
Extended economizer heating surface can reduce the ash surface heating surface abrasion, while heating surface enables a compact structure, reduce air flow resistance and flow resistance of the working fluid, metal consumption is reduced.
Using extended heat to transform the face of the boiler with economizer for under the existing installation space conditions to ensure improved heat transfer.
Reduce flue gas velocity, reducing wear and tear, to avoid fouling and low temperature corrosion, it is one of the most effective measures to improve the work boiler economizer heating surface stability.
Spiral Tube is the use of high-frequency welding method, the strip along a spiral track on the optical tube welding formed. Compared with the annular rib pipe, spiral fin tube materials by fin winding process and high-frequency welding, allows fins and the base pipe pressure melt into one, the contact resistance is approximately zero, can withstand alternating heat stress after welding deformation, so as not to weaken the bearing capacity of the base pipe is conducive to heat transfer from the fins to the base tube wall. Spiral finned tube coiled serpentine tube (elbow part no fins) group as consisting of pipe economizer heating surface that is spiral fin economizer.
Characterization of the structural parameters of spiral fin economizer are:
Base tube diameter spiral fin tube wall thickness; fin thickness, height and pitch; pitch serpentine group lateral, vertical pitch and so on. Economizer spiral fin type can also be arranged in-line staggered arrangement.
If the economizer installation height is limited, you have to use a smaller diameter of the base pipe.
Extended heating surface heat transfer coefficient with the same base pipe diameter light pipe compared to the heat transfer coefficient is reduced. Finned tube heat transfer coefficient is only the same as the base pipe diameter of the light pipe from 82% to 88% of the heat transfer coefficient; spiral finned tube heat transfer coefficient is smaller, only the same base pipe diameter of the light pipe heat transfer coefficient of 45% to 49 %. At the same time: the various types of heating surface heat transfer coefficient with the base pipe diameter increases are reduced. More importantly, with the base pipe diameter increases, the expansion of the heating surface heat transfer coefficient compared with the same base pipe diameter of the light pipe, the heat transfer coefficient decreases the rate has increased.
Heating surface heat transfer coefficient and heat transfer area of the product can appropriately reflect the changes in the structural characteristics of thermal influence of the heat spread face
All extended heating surface heat transfer and energy efficiency is increased compared to the light pipe, but the extent of the heat transfer increases the energy efficiency of different forms of extended heating surface is different. Spiral finned tube heating surface due to its expansion coefficient, so even though the heat transfer coefficient of the smallest, but still the largest energy efficiency of heat transfer.
Meanwhile, the results also show that with the increase in the diameter of the base pipe, all kinds of heating surface heat transfer energy efficiency were all reduced.
Whether or helical fin-type fin-type expansion economizer heating surface heating surface as its wear resistance are improved. This is mainly due to two aspects:
First, change the flow field occurs when the flue gas flowing through the extended heating surface heating surface;
Second, changes in the flue gas flow rate.
After the economizer heating surface in the form of selected small group should be preferred in order to enhance the heat transfer tube diameter energy efficiency and reduce heating surface wear, reducing metal consumption of heating surface tubes. Use a larger base pipe diameter has the advantage of increased wall thickness, more wear-resistant.
The traditional low temperature superheater, low temperature reheater, economizer are used light tube, tube gas side heat transfer coefficient of exile far below the water side of the inner tube or steam. In order to obtain a higher heat transfer coefficient and occupy a smaller space arrangement, often choose the higher gas velocity is designed so that the convection heating surface of the fly ash badly worn. For large boilers, the heat absorption of each segment in terms of height less backpass space, this contradiction is more prominent.
By heat transfer theory, when both sides of the heating surface heat transfer coefficient should be more than three times the difference in heat transfer coefficient smaller side take extended surface technology. Thereby reducing the thermal resistance, increase of the base surface heat flux density, reducing heating surface (weight, volume), it may also be appropriate to reduce the flue gas velocity to achieve in order to reduce heating surface wear.
Low temperature boiler superheater, low temperature reheater and economizer tube gas side heat transfer coefficient of exile side than the inner tube water or steam side are much smaller (reheater difference in more than 3 times, superheater an order of magnitude difference, province Coal is a difference of 1 to 2 orders of magnitude), it is suitable for use in flue gas side take extended surface technology.
High frequency resistance welding spiral finned tube and other types of expansion surface of the tube (such as fin tube, diaphragm tube, patch tubes, etc.) compared with the following distinctive features:
1) fin base line pressure welded into one, solid welding (welding the rate of more than 95%), the contact resistance is extremely small, the base tube strength has been strengthened, the possibility of causing problems due to thermal expansion is also minimal.
2) per unit length of pipe that extended greater surface area (typically more than five times the light pipe), in the same heat transfer is small, so that a substantial reduction in the number of tubes (reduced by about 40% to 50%), saving quality pipe and also reduces the number of pressure components and weld number, thus reducing the chance of exploding and leaking.
3) Since the finned tubes substantially extend the heated area, heat transfer enhancement, making the unit volume can greatly increase the heating surface layout, you can choose lower than the light pipe flue gas velocity, so that the wear is reduced. Even with the same speed of light smoke tube wear is also lighter.
4) in the same space can be arranged more fin and tube heat transfer area, and therefore without the need to expand the rear of the boiler type body conditions may further reduce the flue gas temperature, so that the boiler flue gas temperature is generally high at present problem can be alleviated.