Effect of six kinds of scale inhibitors on calcium carbonate precipitation in high salinity wastewater at high temperatures

Precipitation of calcium carbonate （CaCOs） scale on heat transfer surfaces is a serious and expensive problem widely occurring in numerous industrial processes. In this study, we compared the scale inhibition effect of six kinds of commercial scale inhibitors and screened out the best one （scale inhibitor SQ-1211） to investigate its scale inhibition performance in highly saline conditions at high temperature through static scale inhibition tests. The influences of scale inhibitor dosage, temperature, heating time and pH on the inhibition efficiency of the optimal scale inhibitor were investigated. The morphologies and crystal structures of the precipitates were characterized by Scanning Electron Microscopy and X-ray Diffraction analysis. Results showed that the scale inhibition efficiency of the optimal scale inhibitor decreased with the increase of the reaction temperature. When the concentration of Ca^2＋ was 1600 mg/L, the scale inhibition rate could reach 90.7% at 80℃ at pH 8. The optimal scale inhibitor could effectively retard scaling at high temperature. In the presence of the optimal scale inhibitor, the main crystal structure of CaCOs changed from calcite to aragonite.

Molecular simulation of oligomer inhibitors for calcite scale

Molecular simulation was performed to study the interaction between CaCO3 crystal and several oligomer inhibitors, by using the equilibrium morphology method to calculate the growth morphology of CaCO3 without inhibitors. The calculated morphology agreed well with SEM photographs. Then, a double-layer model was built to investigate the interaction between calcite crystal and oligomer inhibitors containing maleic anhydride （MA） and acrylic acid （AA）. Interaction energy per gram of an oligomer inhibitor was introduced as a scale of inhibition efficiency of different monomers. The results indicated that, for calcite scale inhibition, acrylamide （AM） and vinyl phosphonic acid （VPA） were the most efficient monomers, while allylsulfonic acid （AS） was the poorest. Increasing proportion of AM in dimer inhibitor molecule would improve the inhibition efficiency of MA, though, for a trimer, such as MA-AA-AM, certain sequence of monomers in the inhibitor molecule was necessary besides higher proportion of AM.

Experimental study on the compatibility of scale inhibitors with Mono Ethylene Glycol

When both of the scaling and hydrate risks occur in deep water wells or subsea pipelines at the same time,the compatibility between scale and hydrate inhibitors should be paid more attention to for the risk prevention.In this paper,a new deep-water gas field found in the South China Sea is taken as a reference of project background to investigate the compati bility between scale inhibitors and hydrate inhibitors experimentally.Firstly a preliminary qualification evaluation of scale inhibitors was caried out,in which the static scale inhibition eficiency,the scale induction time,and the minimum effective concentrations of the selected scale inhibitors were tested.Then the effect of commonly used thermodynamic hydrate inhibitor MEG(Mono Ethylene Glycol)on the anti-scaling performance of scale inhibitors was evaluated.MEG-resisted scale inhibitors were further optimized.Finally,an extended discussion on the compati-bility of scale inhibition with hydrate inhibition was conducted.The experimental results showed that the scale inhi bitors HPMA and MA/AA were recommended with the best working concentration of 30 ppm.The high concentration inhibitors(30 wt%)can coexist with the same volume of pure MEG for more than 12-14 h at room condition and 60°C without any precipitation.The anti-scale fficiency of inhibitor with 30 ppm concentration is still up to 90%even at the presence of 20wt%MEG(after2-4 h at 95°C).Hence,in deep-water wellbore,compatible scale and hydrate inhi bitors can be injected together using one chemical pipeline.Besides,it is also found that the polymer scale inhibitors generally have good compatibility with MEG.It deserves further studies and can be regarded as one direction for scale inhibitor improvement in the future.