Pump, recycle

Fig. 38. Caustic purification system a, 50% caustic feed tank b, 50% caustic feed pumps c, caustic feed preheater d, amonia feed pumps e, ammonia feed preheater f, extractor g, trim heater h, ammonia subcooler i, stripper condenser j, anhydrous ammonia storage tank k, primary flash tank 1, evaporator reboiler m, evaporator n, caustic product transfer pumps o, purified caustic product cooler p, purified caustic storage tank q, ammonia stripper r, purified caustic transfer pumps t, overheads condenser u, evaporator v, evaporator vacuum pump w, aqueous storage ammonia tank x, ammonia scmbber y, scmbber condenser 2, ammonia recirculating pump aa, ammonia recycle pump. CW stands for chilled water.

Fig. 15. Ain-saturator systems used in the practice of water treatment by flotation (31). (a), Injection of air into suction line of recycle pump (b), packed...

The major difficulty with these reactors is in the outside recycle pump, especially at high temperatures. Reciprocating pumps require seal rings, and these cannot take the high temperature needed for most reactions. If the recycle gas is cooled down before entering the compressor, it must be reheated before it enters the reactor again. This makes them complicated in construction and excessive in cost. 

Various experimental methods to evaluate the kinetics of flow processes existed even in the last centuty. They developed gradually with the expansion of the petrochemical industry. In the 1940s, conversion versus residence time measurement in tubular reactors was the basic tool for rate evaluations. In the 1950s, differential reactor experiments became popular. Only in the 1960s did the use of Continuous-flow Stirred Tank Reactors (CSTRs) start to spread for kinetic studies. A large variety of CSTRs was used to study heterogeneous (contact) catalytic reactions. These included spinning basket CSTRs as well as many kinds of fixed bed reactors with external or internal recycle pumps (Jankowski 1978, Berty 1984.)... 

The fire was more serious than it would normally have been because the inventory in the plant, about 70 tons, was about twice the usual amount. Some of the overheads from a reactor were collected in a slops drum and recycled. The inventory in the drum was usually small. At about 9 a.m. on the day of the fire, the recycle pump failed. As a result, the level in the drum rose, and the level in the reactor fell. The operator noticed the fall in the reactor level (but not the rise in the drum level) and recycled product to maintain the level. At 8 p.m. the supervisor noticed that the high-level alarm on the slops drum was lit he found that the recycle pump had failed, and he changed over to the spare it leaked 25 minutes later. Section 3.3.1 describes another occasion when operators failed to notice unusual readings for 11 hours. 

Tlie failure rate per year, Y, of a coolant recycle pump has a log-normal distribution. If In Y luis mean, -2, and variance, 1.5, find P(0.175 < Y< 1). Tliree light bulbs (A, B, C) are coiuiected in series. Assume tliat tlie bulb lifetimes are noniially distributed, witli tlie following means and standard deviations. 

ESTIMATION OF FAILURE RATE OF COOLANT RECYCLE PUMP... 

Mosleh, Kazarians, and Gekler obtained a Bayesian estimate of the failure rate, Z, of a coolant recycle pump in llie hazard/risk study of a chemical plant. The estimate was based on evidence of no failures in 10 years of operation. Nuclear industry experience with pumps of similar types was used to establish tire prior distribution of Z. Tliis experience indicated tliat tire 5 and 95 percentiles of lire failure rate distribution developed for tliis category were 2.0 x 10" per hour (about one failure per 57 years of operation) and 98.3 x 10 per hour (about one failure per year). Extensive experience in other industries suggested the use of a log-nonnal distribution witli tlie 5 and 95 percentile values as llie prior distribution of Z, tlie failure rate of the coolant recycle pump. 

Bayes tlicorem and tlie log-normal distribution are used in the first case study (Section 21.2) to obtain an estimate of the failure rate of a coolant recycle pump. 

A SMB, whatever the number of zones, consist of 4 to 24 columns with 3 to 5 pumps and a number of valves, which allow the columns to be connected to different lines. Further discussions are restricted to the classical 4-zone SMB. There are different ways to connect columns in order to build a SMB. An important option is linked to the presence or absence of a recycling pump in order to build a SMB. The examples are shown in Fig. 10.3. 

As shown in Fig. 10.3a, the most classical way is to use a recycling pump that is located between two columns (for instance 12 and 1). The recycling pump, which is... 

A more serious limit to this implementation is due to the volume of the recycling pump and associated equipment such as flowmeters and pressure sensors. As the pump moves with respect to the zones, its volume leads to a dead volume dissymmetry, which can lead to a decrease extract and raffinate purities. This decrease can be significant for SMB with short columns and/or compounds with low retention. However, it can be easily overcome by using a shorter column or asynchronous shift of the inlets/outlets [54, 55]. This last solution is extremely efficient and does not induce extra costs because it is a purely software solution. 

In a different implementation (Fig. 10.3b), the recycling pump is fixed with respect to the zones. It is always located between zones IV and I where no solutes are present. In order to implement this idea, additional valves are needed, which makes the system more complex than the previous one. Its main interest is found when physical modulation is used, as in the supercritical fluid SMB, for which it can be shown that a great interest could be taken from a higher pressure in zone I [56]. The only way to obtain this result is to maintain the recycling pump immediately before zone I. 

As illustrated in Fig. 10.3c, a final solution is to use the eluent pump instead of the recycling pump. This implementation may enable the setup to be simplified, but more valves are required than option a), and a drawback is that one outlet must be recycled to the eluent tank. 

Figure 10.3 Recycling options in SMB systems, a) Recycling pump fixed with respect to the columns, b) Recycling pump fixed with respect to the zones (between Zone IV and Zone I), c) No recycling pump.

Reactor vent cooler is RE-1 Reactor vent condenser is RE-2 Reactor recycle pump is RP-1 Level control valv e is Rl C-1 Relief valve is RSV-1... 

The recycle reactor is shown schematically in Figure 1. It consists of a catalytic or electrocatalytic reactor unit with a bypass loop, a recycle pump and a molecular sieve trap unit. The latter comprises one or two packed bed columns in parallel each containing 2-10 g of Linde 5A molecular sieve pellets. On line gas chromatography (Shimadzu 14A) was used for the analysis of CH4, O2, CO, CO2, C2H4 and C2H6 in the reactants and products. 

There are different ways to connect the columns to build a SMB system. An important aspect is always the position of the recycling pump. The recycling pump ensures the internal flow of the mobile phase. Most often the recycling pump is placed between the last and the first column, i. e. columns 12 and 1 in Fig. 2. Once the recycling pump is fixed with respect to the columns, it moves with respect to the zones and is alternatively located in zones IV, III, II, and I. The flow rates required in the different zones are different and so the pump flow rates vary from... 

Summing up, a robust and easy to handle SMB-design uses 4 zones, a recycling pump fixed in respect to the columns and two pumps for the control of the outlet flow rates. Extremely high precision of all technical components of the SMB is needed. All pumps and valves have to be exactly synchronized. The flow rates should not vary by more thanl % from the preset value. All connections between the different parts of the system must be carefully optimized in order to minimize the dead volume. All columns should be stable and nearly identical in performance. If the SMB-technology is to be used in Biotechnology, GMP issues (cleaning, process and software validation) also have to be considered. In addition and as with any continuous process in that particular area, the definition of a batch could be a problem. 

Interior of ARO System Showing Pressure Vessel (across front). Pressure Pump (at back), Recycle Pump, Valves and Plumbing... 

Fig. 3—in the two stage desalting system, dilution waier is injected between stages. 9reatly reducing the amount ol dilution water required. Further reductions may be achieved by adding the second stage recycle pump... 

Further reduction is achieved by adding the second stage recycle pump. Second stage water is much lower in NaCl than the produced stream inlet water due to addition of dilution water. By recycling this water to the first stage inlet, both salt reduction and... 

Desalter units generally will produce a dehydrated stream containing like amounts of BS W from each stage. Therefore, BS W can be considered pan through volume and the dilution water added is the amount of water to be recycled. The recycle pump, however, generally is oversized to com- >cnsate for difficult emulsion conditions and upsets in the system. 

Minimum suspension criteria for multiimpeller reactors are given by Dutta and Pangarkar [33], Data for venturi-loop reactors are limited [34-35], However, because of continuously sucking the slurry away from the bottom by the recycle pump, possibly not many problems on solids settling occur. 

---