Separations robustness

Owing to its potential of performing extremely high-efficiency separations, robustness of the equipment, automation, ease of use and flexibility, electromigration methods, i.e. CE have widely been applied to different problems in analytical chemistry. It is considered to be a complementary or even an alternative technique to established chromatographic techniques such as HPLC, GC and others. 

Companies such as Rhino and Au Bon Pain can keep their product and process improvements separate. Robust supply chain processes can handle all the types of entertainment and sandwich variations that are likely to be encountered. B and C product development efforts should formally consider the impact on the supply chain. Will it require a B, C, or D response from supply chain managers Or does it require none at all If it does require a B, C, or D response, then a concurrent engineering effort should be initiated. Chapter 29 describes tools for a CE effort. 

Metal and plastic wedge wire screens are commonly used in the construction of filters and other separators, as either the support for finer filter media or as the filtering medium itself. The screens have typical aperture sizes of >50 pm with an average tolerance of 10%. Metal, usually steel, screens are used in applications where separator robustness needs to be combined with slurry dewatering duties or when the solids are particularly coarse or abrasive. 

The use of selectively reduced integration to obtain accurate non-trivial solutions for incompressible flow problems by the continuous penalty method is not robust and failure may occur. An alternative method called the discrete penalty technique was therefore developed. In this technique separate discretizations for the equation of motion and the penalty relationship (3.6) are first obtained and then the pressure in the equation of motion is substituted using these discretized forms. Finite elements used in conjunction with the discrete penalty scheme must provide appropriate interpolation orders for velocity and pressure to satisfy the BB condition. This is in contrast to the continuous penalty method in which the satisfaction of the stability condition is achieved indirectly through... 

In generalized Newtonian fluids, before derivation of the final set of the working equations, the extra stress in the expanded equations should be replaced using the components of the rate of strain tensor (note that the viscosity should also be normalized as fj = rj/p). In contrast, in the modelling of viscoelastic fluids, stress components are found at a separate step through the solution of a constitutive equation. This allows the development of a robust Taylor Galerkin/ U-V-P scheme on the basis of the described procedure in which the stress components are all found at time level n. The final working equation of this scheme can be expressed as... 

The typical phase equiHbrium problem eacouatered ia distiHatioa is to calculate the boiling temperature and the vapor composition ia equiHbrium with a Hquid phase of specified composition at a givea pressure. If the Hquid phase separates, thea the problem is to calculate the boiling temperature and the compositions of the two equiHbrium Hquid phases plus the coexistiag vapor phase at the specified overall Hquid compositioa. Robust and practical numerical methods have been devised for solving this problem (95—97) and have become the recommended techniques (98,99). 

Teirrperamre is often a forgotten variable in HPLC but ean influenee the robustness and seleetivity of many separations or if exploited eair provide novel high temperature separation eonditions with either high effieieney, a unique seleetivity or enable new deteetion methods to be applied. 

If uneontrolled, temperature ean have a signifieant effeet on reprodueibility and the robustness of separations. This ean eause major problems in metlrod transferability between laboratories and at its worst ean require a method to be reoptimised or revalidated. Most separations therefore require a tlrermostated environment. However, the important faetor is tire temperature witlrin the eolumn bed, not just the sunounding enelosure. Cireulating ah ovens, statie air ovens, metal bloek heaters and eireulating water baths ean all generate different effeetive temperatures even if set to the same nominal values. 

With a steam turbine, the turboeompressors ean be readily matehed to the different plant operating eonditions. Under eontinuous load, this type of installation is powered by the steam resulting from ammonia eombustion. Consequently, an outside steam supply is needed for startup. This may be a separate boiler or another external souree with live-steam properties not neeessarily eorresponding to those obtained from the nitrie aeid plant. The steam turbine must be of robust design beeause of the different pressure and temperature levels. 

The most important application of semi-permeable membranes is in separations based on reverse osmosis. These membranes generally have pores smaller than 1 nm. The pressure across the semi-permeable membranes for reverse osmosis is generally much larger than those for ultrafiltration, for example. This is because reverse osmosis is usually used for small molecules which have a much higher osmotic pressure, because of the higher number density, than the colloids separated in ultrafiltration. As a result reverse osmosis membranes have to be much more robust than ultrafiltration membranes. Since the focus of our discussion in this chapter will be on reverse osmosis based separations, we will describe these membranes in greater detail. 

Storti G., Mazzotti M., Morbidelli M., Carra S. (1993) Robust Design of Binary Countereurrent Adsorption Separation Proeesses, AIChEJ. 39 471-492. 

The above conditions are not robust because they are at the limit of the complete separation zone. The equilibrium theory neglects the dispersion phenomena and therefore the purity obtained under these flowrate conditions would be less than 100 % on a TMB system. Complex simulation software, which takes into account the dispersion phenomena, gives a more robust system with higher purities [57]. 

A.c. impedance. Measurements of the frequency variation of impedance allow separation of the change transfer resistance from the contributions to the total impedance of the environment resistance, surface films, adsorbed layers, etc. Robust instruments utilising a two-frequency technique have been developed . 

Since the end product is to be useful heat, there is an opportunity with heat pump compressors to use a drive motor which will contribute to this. The internal combustion engine is used for some drives, adding its radiator heat to the load, and at a higher temperature than the refrigerant condenser can provide. As the installation is static, and required to run for comparatively long times without attention, the ideal fuel is natural gas. Compressor and drive assemblies must be robust to withstand the extra vibration, and should be separate from the rest of the circuit. Engine combustion air intakes must be from outside the plantroom and possible refrigerant leaks. Steam drives have also been used. 

So-called combination electrodes may be purchased in which the glass electrode and the saturated calomel reference electrode are combined into a single unit, thus giving a more robust piece of equipment, and the convenience of having to insert and support a single probe in the test solution instead of the two separate components. 

When assessing the robustness of a process, several factors that can adversely affect it include non-selective or side reactions that might produce adverse effects and impurities physical and chemical stability of the materials involved and complexity of the separation train of the processes. 

---