Why are the superheater tubes arranged in parallel, while the economizer tubes are arranged in staggered fashion?

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I wonder if anyone has noticed that the arrangement of the tubes in the economizer and the superheater is different: one uses a straight arrangement while the other uses a staggered arrangement. Those who haven’t noticed can take a look during maintenance. So what causes this difference? Let’s analyze it below. Friends who would like to discuss this further are welcome to leave comments or join the group. Superheaters are usually installed in areas where the flue gas temperature is high. Convective superheaters are mostly placed in the horizontal flue gas ducts right next to the furnace outlet, while screen superheaters are typically located near the furnace outlet as well. When designing boilers, it is required that the flue gas temperature at the furnace outlet be 100–DT50°C lower than the deformation temperature of the ash from the coal being used, in order to prevent slag formation in the superheater tubes. However, when the fuel changes or the water wall suffers severe coking, the ash in the flue gas at the furnace outlet may reach its softening temperature and become sticky. Therefore, in order to avoid or reduce the sticking of ash to the superheater tubes, and also to facilitate the support and suspension of these tubes, superheater tubes are usually arranged in a parallel configuration. In a economizer, the flue gas temperature is much lower than that at the furnace outlet, so there is no issue of ash sticking together. It is necessary to comprehensively consider which offers higher economic benefits, permutations or derangements. The economizer tubes are arranged in a staggered pattern; since the back side of the tubes is also prone to being eroded by ash particles, ash accumulation is minimal. In a straight arrangement, since the back side of the tubes is not easily subjected to ash particle erosion, and even the front side of the tubes is less prone to such erosion, ash accumulation on the tubes in this arrangement is relatively severe. If the longitudinal pitch of the staggered tubes is reduced, the dust accumulation on the leeward side can be reduced due to more intense erosion on that side ； In the case of pipes arranged in a row, the reduction in the longitudinal pitch not only fails to reduce dust accumulation but actually makes it worse. When the tubes are arranged in a staggered pattern, the disturbance and erosion exerted by the flue gas on the tubes are greater than when they are arranged in a straight line; therefore, the heat transfer coefficient on the flue gas side is higher in the staggered arrangement. Since the heat transfer resistance of the economizer is mainly on the flue gas side, arranging the economizer tubes in a staggered pattern can improve the heat transfer coefficient and reduce the required heat transfer area. Although the staggered arrangement of the economizer tubes increases ventilation resistance and raises the power consumption of the induced draft fan, the clean heat-exchanging surfaces result in low thermal resistance and high heat transfer coefficients, which allows for a reduction in the heat transfer area of the economizer and thus saves on investment; the advantages outweigh the disadvantages. Therefore, the economizer tubes are usually arranged in a staggered pattern.