Merrow Scientific Blog

Great value for money high pressure stirred reactors!

Merrow Scientific are the UK representative for Autoclave Engineers, who have been designing and manufacturing high pressure systems since the 1940s. 

Autoclave Engineers, who lead the way in terms of innovation, design quality and custom configuration, also lead in terms of value for money!  Sure there are companies who'll offer to make a pressure vessel or stirred reactor for a slightly lower price, but I wonder if these same companies can say they've never had a failure of a vessel in their 70 year history, or that they have customers running stirred reactors still that were supplied in the 1960s?

All Autoclave Engineers systems have serial numbers on all components, metal to metal precision engineered seals used on all VFT components, and all systems supplied since the 60s have detailed drawings in pdf format quickly available.  These makes it easy to keep all of our customers, even those with 50 year old systems, supplied with spares when needed.

One benefit of metal to metal engineered seals on the VFT is the fact that this means there are no welded ports (when they break that's it for the reactor), no teflon tape and compression threads (not a high temperature or precision pressure sealing method), so when a customer needs to replace a component they can do that easily and quickly.

So the return on investment when a £10K reactor lasts for over 50 years is pretty impressive!!

Experts in high pressure vessel manufacture

Our US partner Autoclave Engineers have yet again proven themselves to be leading the world in the design and manufacture of high pressure equipment.

Terms such as "experts", "leading the world" and even "high pressure" are often used in marketing speak without really much substance, so let me back up my statement with a couple of bits of information:

• Autoclave Engineers have been in this business of designing and manufacturing high pressure vessels, stirred reactors, VFT and other pieces of equipment since the 1940s and have never had a failure!  They have been certified to the highest levels of the PED (pressure equipment directive - law in the EU for the supply of pressure vessels), ASME and other pressure equipment legislation.
• A good example which illustrates their high levels of competence perfectly is one of their latest vessels.  This was to meet a requirement for a company supplying components for oilfields - they needed to test the components at high pressures and raised temperatures to check their performance before they were used in the field where those conditions would be experienced.   The vessel supplied was required to be operated at 40,000 PSI and 260degC, and due to the size of the components to be tested the vessel had to be 45 feet long and 15" ID - so a large high pressure system indeed.  The below pictures show the vessel being moved by crane lift and also the pressure gauges during the testing cycles (yes that's 60,000PSI they're being tested at!! Really shows the safety margins factored in).

So when it comes to high pressure vessels - Autoclave Engineers really are experts and leading the world.  If you'd like any further information please don't hesitate to contact us (Merrow Scientific are the UK partner for Autoclave Engineers' vessels and reactors) or look at our pressure vessel page.

Check your bearings! (at least every so often please….)

From time to time we get a call from one of our customers who has an Autoclave Engineers stirred reactor in their lab to let us know that the system has started to make a weird squeaking noise.The first question we ask is “when did you last check the bearings?” – this is normally met by silence on the other end of the line… (so you’re not alone!!)

So let’s start off with a few basics, beginning with a photo of an example reactor, the mini reactor from AE (small scale stirred reactor rated to 200 bar and 315degC):

As you can hopefully see the arrangement is something like this:

• » Inline motor at the top, which is connected to the
• » Magnedrive magnets, these spin round at your required and specified rpm and through the cover (via the magnetic field coupling) accurately rotate the
• » Encapsulated inner magnet assembly which leads to the
• » Shaft and impeller

So the cover means that the reactor is a completely sealed environment and the use of the magnets allows accurate and positive control of the stirring of the product inside the reactor.(hope that makes sense!)This is the same throughout the range of reactors although sometimes the motor can be bigger and linked to the magnedrive via a belt. (more…)

Magnetic Attraction!!

Two of our main product ranges that we supply in the UK market greatly benefit from the use of powerful earth magnetic technology.

Autoclave Engineers first developed and launched their magnedrive powered laboratory stirred reactors back in 1958 leading the world in this development. This was a way of having a sealed reactor free from risk of leakage or contamination that could be accurately stirred even when run at high pressures. This was achieved using a magnet coupling between driver magnets (rotated by an motor) and an encapsulated inner magnet assembly which leads to a shaft and impeller, so as the driver magnets are rotated the impeller and shaft are also rotated. Such are the strength of the magnets used that accurate controlled stirring can be achieved even at high torque requirements and under high pressures or temperatures.

The other excellent use of magnets comes from Rubotherm. Many years ago the research team in the Thermodynamics dept at the Ruhr University in Bochum had a project requiring gravimetric analysis of samples at raised pressures. Conventional gravimetric systems have a direct connection between the precision balance and the sample - which is great for low pressure applications, but once you get above 20bar or so or start to look into things like corrosive vapours then you get a bit stuck as your balance is in the same area as the sample you wish to subject to the high pressure etc, and doing so will damage the balance, so conventional systems weren’t any use.

So using a magnet/electromagnet coupling, a position sensor and a cracking control system they devised a magnetical coupling gravimetric system for measuring mass change/transfer of sample while subjected to a wide range of conditions.

This technology was eventually patented and a spin off company formed (Rubotherm). Systems have now been supplied all over the world for a variety of applications, including gas storage (e.g. hydrogen, CO2 or Methane into zeolites or MOFs), corrosion testing, biomass and coal gasification, polymer degradation and lots more. We’ve been up to pressures as high as 2000bar, temperatures as high as 1600degC and no problem at all dosing corrosive things over samples and measuring mass change.

The latest development allows TGA type measurements at raised pressures. Why would you want to do that? Well with some applications it allows you to imitate the real life conditions that would effect your sample and measure accurately what happens, for example HP TGA on oil, biomass or coal gasification, degradation of materials used in off shore drilling….. This hasn’t been possible until now as other TGA systems only operate at atmospheric pressures.

So thanks to the attraction of the magnet our customers in the UK are able to push their research into new and exciting areas……

Plumber’s tape?

If you google Teflon Tape the very first result is the wikipedia page that describes Teflon tape as

“Thread seal tape — commonly known as “Teflon tape”, “PTFE tape”, “tape dope”, or “plumber’s tape” — is a polytetrafluoroethylene (PTFE) film cut to specified widths for use in sealing pipe threads. The tape is wrapped around the exposed threads of a pipe before it is screwed into place. Since the PTFE is malleable, deformable and impermeable, it acts a little like putty under compression, being forced into small gaps between threads in order to create an air- and watertight seal when threaded into a joint. The tape is commonly used commercially in pressurized water systems, such as central heating systems, as well as in air compression equipment and thread joints with coarse threads.”

And then futher on in the same chapter

“Over-use, or mis-application of thread tape may be a hazard. As the tape material is so soft, excess or overhangs may easily break off and form a foreign body contaminant that could jam a valve seat etc.

Thread sealing tape is almost entirely applied by hand, owing to the ad hoc nature of most repair work”

Teflon also has a melting point of around 327degC, but its properties degrade above 260degC according to DuPont (the manufacturers of teflon).

We get asked about this a lot, so let me explain, the Autoclave Engineers range of reactors that we supply in the UK (see our Merrow Scientific reactor page) use a Metal to Metal engineered sealing for all of their valves, fittings and tubing, so no teflon tape.

The benefits of this method include:

• » Precise, repeatable and highly rated sealing
• » All parts are serial numbered so you can easily swap or replace
• » High temperatures and extremely high pressures are no problem
• » No welding (which could potentially have weak points which could lead to failure under pressure and are permanent and not easily replaced or repaired)
• » And no plumber’s tape……