DDT EXPERTS

 and

Combustion Hazard Research

SPECIALIST CONSULTANCY SERVICES ON DETONATION,DEFLAGRATION TO DETONATION TRANSITION(DDT) AND RELATED INDUSTRIAL PROCESS SAFETY HAZARDS

click here for more details about ddtexperts

 

 

 


find out more

why us?

Mission statement

 services  available   

who are we?

contact details

video archive    

publications and presentations

Examples of previous successful projects

Example of the appplication of a computational fluid dynamics tool

 


 

 WHY  DDTexperts?

Mission Statement

 

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Services available:

     I)    Preparation of consultancy reports to identify and review relevant Scientific issues

II)    The development, implementation or project management of bespoke experimental test programmes*

    Routine experimental testing , in accordance with accepted procedures and standards.

*    when necessary we can co-ordinate a tendering activity amongst  other testing organizations/laboratories to ensure the best solution for our clients

III)      The analysis and interpretation of experimental test results together with suggestions for solutions to alleviate problems identified.

IV)    Supervise Investigations of the efficacy of mitigation/prevention solutions.

V) Preparation of independent reports for submission to Health and Safety Organizations or explosion certification Notified Bodies as required

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 Publication policy.

In accordance with our aims of  researching, applying and disseminating latest good practice and scientific/technical knowledge to ensure maximum safety  in process industry applications we strive whenever possible to publish suitable scientific and technical findings in the open literature.

Every such publication submission is always made with the full approval of the client that initiated and sponsored the study.

 Please click her to link to a list of   External publications and presentation

HOT OFF THE PRESS:

For copies of the most recent papers, in print or accepted for publication please click here

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Video archive

why not let us amuse you by watching some of our  archived  test videos  which also highlight some of the more serious sides of   the commercial industrial explosion studies we have  undertaken over the years.

 Unfortunately some of these filesmay be too  too large to view online. if you are still interested please email and  ask for a CD copy of this web site:  reprints@ddexperts.com

 Click on the following image  to play a video of how we like to let off steam from a hot water tank incorrectly  installed on a small  plearure boat

  and this is what happens with the tank alone                               

 

click on the image below  to see how we helped one small company  based in the Wirral  avoid being caught on the hop!

  

Please note that after this test the reactor vessel was licensed as safe by the relevant safety directorate, as we were able to demonstrate that theduplicate prototype the client  supplied could withstand   a representative explosion in the reactor volume with no evidence of catastrophic damage. The vessel hops because of momentum transfer to the liquid in the large horozontal quench tank from liquid injected from the lower part of the vertical reactor section. discharged through a bursting disk. The equipment suffered only minor damage, mainly mechanical deformation of the lower quench tank where it wasjoined to the rear foot, directly beneath the vertical reactor vessel.

 or why not watch an ethylene-air detonation propagate along a 300 mm diameter Glass Reinforced Pipeline   and again wherethe detonation is  brighter

Alternatively how about quick time movie from a numerical simulation of the propagation of a detonation past a junction provided courtesy of our one of our  CFD collaborators, located at Porsgruun University, Norway.  Then, click on the image below to see

how they tried successfully  to  reshape a shipping container using hydrogen

     

 Directors note : no clients, staff members, Fish, Reindeer or Sheep  were hurt during the making of these films

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Examples of previous successful projects

dynamic mechanical response

 mitigation of offshore explosions by water sprays

marine hot water tanks

flame propagation and detonation limits

application of computational fluid dynamic techniques to support experimental investigations

detonation arrester testing and certification

Process pipe integrity

a well known  UK chemicals company was concerned about whether a process vent manifold, feeding a thermal oxidiser, could withstand a detonation initiated  in the  oxidizer combustion chamber. Experiments with a representative gas mixture ( ethylene-air) showed that a GRP pipe survived but that a HDPE pipe(residue shown below) could not,most probably because of embrittlement resulting from the high Carbon loading used to increase electrical conductivity in an attemp to improve overall safety performance by minimizing the likelihood of static spark ignition of the gases contained in the vent manifold.

 

                                         

 

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 safety of marine hot water storage tanks.

A small manufacturing company required assistance to help it demonstrate the consequences of not fitting the correct pressure and temperature sensors to a hot water storage tank on small marine boats. the  images below are views   of the  controlled failure of a 35l tank of near boiling water.

 

BEFORE

DURING

AFTER

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Mechanical response to detonation loading .

 A major UK company wished to evaluate the performance of its in-house finite element modelling of the response of materials to dynamic loading.

A series of tests were developed where a thin stainless sheet was used to seal one end of a pipe containing a detonable mixture. The time resolved impulsive motion of the plate in response to the dynamic loading as the detonation wave reflected at the test plate end was monitored successfuly using strain gauges spaced along a diameter and the residual deformation photographed.

 

As the pipe length was increased the nature of the deformation altered until there was first failure at the plate mid point.and then as the length of detonable mixure was increased further( thus increasing the total impulse) a point was reached where the plate sheared completely at its periphery.

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Droplet break up and mitigation of offshore explosions.  

 In an extended work program sponsored by the United Kingdom health and safety executive, Mobil North Sea and British Gas a series of small-scale experiments investigated the mechanisms by which general area water deluge was effective in mitigating explosions inside offshore oil rig modules[ access HSE report in pdf format here]

To confirm the theory that the controlling factor was the inertia of large droplets in the gradually accelerating gas flow in front of the explosion combustion front a further series of laboratory experiments were conducted in a modified shock tube. These photographic results (examples of which are show below) demonstrated conclusively that explosion mitigation resulted from the extremely fine residual droplets formed as the large initial drops were destroyed by the forces caused by the velocity difference between the a large drop and the transient accelerating gas in which it is immersed. The findings of the study suggested strongly that the fine mists commonly used for fire-fighting applications would not be suitable for mitigating offshore explosions and that significant attention should be paid to developing new spray delivery systems with specific  droplet size distributions

 

 

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 Flame propagation and detonation limits

Several companies have required assistance to allow them to determine safe operating conditions for chemical synthesis processes. Usually these have involved fuel-oxygen mixtures at elevated temperatures and pressures. In nearly all instances safe operating conditions have been successfuly identified by computing certain detonation properties, most particularly estimations of detonation cell widths.  The limit can then be identified by a critical ratio of cell width to the tube diameter

Experiment confirmed that these limits could be observed in practice

The results shown immedeately below are from a study of ethylene-oxygen mixtures with initial pressures up to 7 bar absolute and a gas temperature of up to540 K  

here Predicted cell sizes can be compared with a critical mutliple of the tube diameter and against experimental data of observed overpressure. Other systems studied in this manner include methane-ammonia-oxygen as well as methane-hydrogen-oxygen. In addition transition to detonation data has been obtained for fuel-air mixture in pipes of diameter 150 and 300 mm

 

 

 

Predicted detonation cell widths based on auto-ignition delay times at von Neumann temperatures and pressures.

Initial pressures 1 and 7 bara (initial temperatures 293 or540 K)

 

Peak overpressure measured in a7 mm tube as a function of oxygen concentration for

ethylene-oxygen mixtures at  7  bar and 393K

  

Experimental observations of flame position with time for initial flame acceleration in a 30 m long 150 mm diameter steel pipe.

All fuel mixtures are  stoichiometric with air.

Only  hydrogen and ethylene underwent a transition to detonation, at much later times than those shown above.

detonation arrester certification

Whilst director of the centre for explosion studies at Aberystwyth , Dr. Geraint Thomas was responible for  supervising investigations that contributed directly to the present European Standard [ BS EN12874]  used to certify detonation and deflagration arresters

The following(right) is a frozen frame Image  from a night-time high speed video obtained  during the initial  development stages of an end of line detonation arrester. The image on the left shows the test setup in daylight,click here to see the entire daylight video

    

The Figure below shows experimental pressure gauge outputs from a succesful test of an in-line  detonation arrester when subjected to an overdriven detonation. The graph shows records from two pressure gauges before the arrester and from two further  gauges beyond it, both of which exhibit much lower pressure levels demonstrating the effectiveness of the arrester. The theoretical peak detonation pressure is ca. 18 barg

 

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 computational fluid dynamics;

   

Although not an expert in the techniques of computational fluid dynamics himself,  Dr. Geraint Thomas has always appreciatedthe benefits  that can be derived from the measured applicationof computational fluid dynamics techniques to complement experimental investigations .As an example,since he established DDT experts in 2005 he has maintained  close contact with friends and colleagues in Norway who have assisted him with simulations of detonation diffraction and propagation from a straight pipe pipe across a larger cross-section cylindrical volume. These initial 2-D calculations were then extended to investigate the operation of  of a novel detonation mitigation device based on a matrix of cylindrical  rods aligned perpendicularly to the original incoming detonation wave. Such simulations provide valuable insights when developing a targeted experimental research programme during the development of a novel detonation arrester design.  

 click her for a CFD simulation of a detonation diffracting into a cylindrical volume  

whereas this simulation illustrates how the initial detonation structure is disrupted

by the inclusion of a matrix of aligned rods

                                 

 

 

CFD can also assist in interpreting  experimental observations.

The following simulation is of a detonation propagating past a side branch in a pipe before reflecting off a closed end

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Not only do such simulations inform us about the propagation mechanisms, they can also provide data on the net loads for use in finite element modelling of the  mechanical response of the pipe and its supports

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  Principal Consultant:

Dr Geraint Thomas(phd(wales), I.Chem.E., A.I.Chem.E.)

The principal  scientific consultant is Geraint Thomas who has personally worked with and has specialized on gas detonation and related explosion phenomena since 1974. In addition to his personal knowledge he can also call on and coordinate the skills and knowledge available amongst his many friends and former colleagues world-wide. Thus although he may not always be able to personally deliver the solutions  required to provide answers to specific  problems he is uniquely placed to act as a conduit to other personnel and their individual specialized resources/experience. Further, he has the necessary proven explosion project management experience to successfully muster and coordinate inputs from a range of sources on behalf of clients and report back to them.

DTExperts is part of a private consultancy service started by Dr. Geraint Thomas. It and the sister project management activity Consultancy on Explosion safety  Testing (CEXT) are natural extensions of his initial consultancy activity (Combustion Hazard Research) which was first established in 1986 and which later operated in parallel with his role as the head of the Shock and Detonation Physics research group and director of its Centre for Explosion Studies at the University of Wales Aberystwyth.  

Geraint no longer has any formal links with the University of Wales, nor with any subsequent explosion related activity instigated by the physics department and University at Aberystwyth after his retirement in 2004. He does however continue to have close working links with former key University research colleagues at the Centre for Explosion Studies with whom, in 2006, he established the experimental explosion safety testing company Aber Shock and Detonation Research Limited.

His current formal academic affiliation is with the University of Leeds where,   as of 1 March 2005, he is an honorary visiting Senior Lecturer in the Energy and Resources Research Institute in the school of Proces, Environmental and Materials Engineering

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Contact details

If you wish further details or you would like to  discuss a specific explosion or detonation problem

please contact me via using the options below

Surface Mail:

DDTExperts

POBox 217

Llanerch Bron Padarn

Aberystwyth

UK SY23 3XT

Landline: +44 02921 250732

email : geraint@ddtexperts.com

or in case of difficulties with any the above

Tel  (mobile): +44 07974 924 335

If you have a techical query please submit a brief outline summary of the problem as you see it . I will then contact you directly to clarify specific issues.  Please note that I will happily sign  a non-disclosure agreement or another form of confidentiality document before proceeding with further discussions , if you so desire.

Initial informal queries  are always be treated in the strictest confidence.

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