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

甘蔗乙醇工厂使用石灰添加到原提取汁中，以中和和澄清汁。这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。这导致这些盐作为硬垢沉积在蒸发器中的管的内部上，在蒸发器中通过煮沸水来浓缩糖汁。硬垢会降低蒸发器的传热速率，最终导致管道堵塞。巴西的正常做法是每周手动清洁蒸发器。这涉及人员被降低到蒸发器的上腔室中，并通过“棒化”（即，内管表面的物理磨损）来去除结垢。这不仅涉及在有限空间中的不期望的工作，而且还不可避免地导致管上的显著磨损，从而导致管的频繁更换。在劳动力最昂贵的国家，曾尝试过化学清洗，但结果好坏参半。一个困难是涉及如此多样的钙盐，需要一系列不同的（并且相互不相容的）化学清洁剂，包括强碱，以去除沉积物，因此每次需要几个循环的清洁，并且一些化学清洁剂还引入了额外的危害。此外，每一级蒸发器都有不同的结垢物组合，需要不同的处理方法。该项目是BP集团研究部对此问题的回应之一，旨在找到处理蒸发器管道内部（以及其他潜在的脆弱表面）的方法，使钙盐不会在这些表面上成核。应当理解，水的蒸发必然会使果汁超过有关盐的溶解度极限，因此目的必须是确保盐要么在本体中而不是在表面上结晶，要么形成容易从表面分离的固体而不是形成硬垢。在实际实施中，这将需要在蒸发器下游安装过滤或沉降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.