Surface Modification of Metallic Reaction Vessels to Resist Scaling by Calcium Salts

甘蔗乙醇厂将石灰添加到原始提取的汁液中，以中和和澄清汁液。这会导致果汁被一系列钙盐饱和，特别是硫酸盐、磷酸盐、硅酸盐和草酸盐。这导致这些盐在蒸发器中的管子内侧以硬垢的形式沉积，在蒸发器中，糖汁通过沸腾从水中浓缩。硬垢降低了蒸发器的传热速度，最终会导致管子堵塞。巴西的正常做法是手动清洗蒸发器，每周一次。这包括将人员降到蒸发器的上腔，并通过“拉杆”来清除结垢，即对内管表面进行物理磨损。这不仅涉及到在受限空间中进行不受欢迎的工作，而且不可避免地会导致管子严重磨损，从而导致频繁更换管子。在劳动力成本最高的国家，已经尝试过化学清洗，结果好坏参半。一个困难是，涉及的钙盐种类繁多，需要一系列不同的(且互不相容的)化学清洗剂来清除沉积物，包括强碱，因此每次都需要几次清洗，而且一些化学清洗剂还会带来额外的危险。此外，每个蒸发器阶段都有不同的结垢剂组合，需要不同的处理。该项目是BP Group Research对这一问题的回应的一部分，旨在寻找处理蒸发器管内部(以及可能存在的其他易受攻击的表面)的方法，使钙盐不会在这些表面上成核。可以理解的是，水的蒸发必然会使果汁超出有关盐的溶解极限，因此目标必须是确保盐要么在块状结晶而不是在表面结晶，要么形成容易从表面分离的固体，而不是形成坚硬的鳞片。在实际实施中，这将需要在蒸发器下游安装过滤或沉淀设备，以收集这些钙质沉淀物。

Sugar cane ethanol plants use the addition of lime to the raw extracted juice in order to neutralise and clarify the juice. This leads to the juice becoming saturated with a range of calcium salts, notably sulphate, phosphate, silicate, and oxalate. This leads to the deposition of these salts as a hard scale on the insides of the tubes in the evaporators, where the sugar juice is concentrated by boiling off the water. The hard scale reduces the heat transfer rate in the evaporators, and would eventually lead to blockage of the tubes.Normal practice in Brazil is for the evaporators to be cleaned manually, as often as weekly. This involves personnel being lowered into the upper chamber of the evaporators and removing the scaling by "rodding", i.e. physical abrasion of the inner tube surfaces. Not only does this involve undesirable working in confined space, but it inevitably also leads to significant wear on the tubes leading to their frequent replacement. In countries where labour is most expensive, chemical cleaning has been attempted with rather mixed results. One difficulty is that such a diverse range of calcium salts is involved, a range of different (and mutually incompatible) chemical cleaners, including strong alkali, are needed to remove the deposits, so several cycles of cleaning are required each time, and some of the chemical cleaning agents also introduce additional hazards. Furthermore, each of the evaporator stages has a different combination of scalants, and requires different treatment.This project forms part of BP Group Research's response to this issue, and seeks to find means of treating the insides of evaporator tubes (and potentially other vulnerable surfaces) such that the calcium salts do not nucleate on those surfaces. It is understood that the evaporation of water must inevitably take the juice beyond the solubility limit of the salts concerned, so the aim must be to ensure that the salts either crystallise in the bulk rather than on the surface, or form solids which readily detach from the surface rather than form hard scales. In a practical implementation, this would require installation of filtration or settling equipment downstream of the evaporators to collect these calcareous precipitates.