Mineral precipitates, scales, are wide-spread in geothermal facilities and hamper technical and economic efficiency. Scales reported from earlier studies in the Bavarian Molasse Basin consisted mostly of calcite, appeared rather homogeneous, grew flat and perpendicular to the surface, and showed little or no internal macrostructure apart from small gradients in crystal size and chemical composition. In this study, we investigated extraordinary calcite scales collected from the inlet chamber of a heat exchanger. These scales showed current ripples and a sequence of coarse and dense layers. By an extensive investigation of the ripples, the hydrochemistry, and by the application of existing empirical equations, the formation of the ripple scales could be reconstructed: Due to degassing of $${\text {CO}}_{2}$$ in the geothermal pump calcite scales precipitated on the pipes of the ground-level facilities. During maintenance works, these scales were partially dissolved, and remobilized as individual mobile grains. These particles subsequently settled again, and solidified as ripple scales in the horizontal pipes at surface level. For this ripple forming process, flow had to be small, because otherwise the ripples would have been altered or washed away. After deposition of the ripple structure, a dense new calcite layer precipitated on top of the ripples, and stabilized it due to transitory supersaturation. This sequence of ripples and a dense calcite cover layer is repeated two times. Finally, during start-up of regular plant operation, the whole composite scale was remobilized and got washed into the inlet chamber of a heat exchanger. The investigation presented here indicates that this type of calcite scale only forms in geothermal facilities in the Bavarian Molasse Basin if certain flow and hydrochemical conditions are present during the maintenance procedure.

中文翻译：

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巴伐利亚州莫拉西盆地地热设施中的波纹状鳞片：了解方解石结垢过程的关键

矿物沉淀物，水垢在地热设施中广泛传播，并阻碍了技术和经济效率。巴伐利亚Molasse盆地早期研究报告的鳞片主要由方解石组成，看上去相当均匀，生长平坦且垂直于表面，除了晶体尺寸和化学成分的小梯度外，内部宏观结构很少或没有。在这项研究中，我们研究了从换热器进气室收集到的特殊方解石水垢。这些刻度显示了电流纹波以及一系列的粗糙和致密层。通过对波纹，水化学的广泛研究，以及通过使用现有的经验方程式，可以重构波纹鳞片的形成：由于地热泵中的$$ {\ text {CO}} _ {2} $$脱气，方解石垢在地面设施的管道上沉淀。在维护工作期间，这些秤被部分溶解，并作为单个的可移动谷物重新运输。这些颗粒随后再次沉降，并在水平面上的波纹管中固化成波纹状。对于这种波纹形成过程，流量必须很小，因为否则波纹会被改变或冲走。波纹结构沉积后，致密的新方解石层在波纹顶部沉淀，并由于瞬时过饱和而使其稳定。此序列的波纹和密集的方解石覆盖层重复两次。最后，在正常工厂运营期间，整个复合秤被重新固定并被冲洗到热交换器的进气室中。此处进行的研究表明，如果在维护过程中存在某些流动和水化学条件，则这种方解石水垢仅在巴伐利亚Molasse盆地的地热设施中形成。