Using Sonar Technology in Re-Defining Profiling/Quantification of Sludge in Crude Oil Tank
An Interferometric sonar is now being used to provide clients with an accurate sludge volume and an image of the sludge build-up in crude oil storage tanks.
Petro-Base Group (under an exclusive license by Willacy Oil Services) has begun using the latest version of the SPOT (Sludge Profiler of Oil Tanks) designed and manufactured by Marine Electronics.
Following improvements with the SPOT system, Willacy has been able to conduct surveys in the UK and worldwide faster and more efficiently than before.
The surveys are important as sludge accumulation can reduce a tank’s storage capacity and cause production problems further down the refining process. Large sludge banks are a particularly serious concern when landing the roof of floating roof tanks as they can cause them to tilt and jam. Such incidents can create a hazardous situation that will prove challenging and expensive to rectify.
Willacy Oil Services has consequently been undertaking regular surveys for clients, particularly when tanks are due for maintenance or when production problems are experienced and also as part of the routine monitoring of sludge build-up and mixer efficiency. Willacy Oil Services has been able to assist refinery and tank farm operators by using this latest technology. The first version of the SPOT sonar was developed in 1995 by Marine Electronics and Willacy Oil Services in conjunction with Bath University. It uses an advanced 3D sonar transducer that is introduced into a full tank of oil through an access point as narrow as 4-inches and which then opens automatically to the correct angle for use. The system is ATEX certified and intrinsically safe for use in hazardous areas.
Surveys are typically performed at up to three access points on the tank where the transducer is rotated robotically through 360 degrees. The latest version of the SPOT sonar has halved the time taken to collect the data, whilst at the same time collecting better quality data.
‘This is a big bonus for the survey operator and for customers,’ Myron Jones of Willacy Oil Services explains. ‘This is because the tanks are taken out of service for the duration of a survey and the window of availability is often very limited. When a tank is needed online at short notice the fast survey time of this system enables us to collect the data quickly and get the tank back in service with the least delay.’
The sonar beam has a range of around 30 metres, depending on the density of the oil and it sweeps the sludge surface with up to 240,000 soundings. The processed acoustic echoes create a highly accurate profile of the sludge inside the tank and a computer in our accompanying survey vehicle can produce an easily interpreted display. This will show sludge heights that are colour coded to represent different levels. Interpretation is helped further by the display of a cross section of the sludge profile that corresponds with the current direction of the transducer.
‘Clients find this data valuable as it enables them to identify potential problems, determine the safest and best method of targeting the removal of sludge banks and also to estimate the costs involved in removing and processing the sludge,’ Jones explains.
A tank survey can easily be completed in one day and at 25kg the light weight of the SPOT sonar makes it easy to deploy and operate by a crew of two. The system uses purged pressurisation and encapsulation protection, being totally sealed and filled with nitrogen. It also has an automatic power shut down mechanism that isolates the system if the nitrogen pressure starts to drop.
The SPOT system has full ATEX certification and the technology is well proven both in the UK and overseas. Earlier SPOT systems are currently in regular use at refineries and tank farms worldwide.
Before the advent of the SPOT sonar, sludge could only be measured by personnel dipping a measuring stick through access points in the tank roof. This is a very slow process usually carried out using breathing apparatus and involves work in a confined space.
The manual method is therefore hazardous and notoriously unreliable. Sludge can accumulate very unevenly in peaks and troughs making accurate measurement of its volume impossible to obtain in this manner. By providing a 3D image of the tank’s contents SPOT overcomes these problems so that a genuine understanding is achieved. Nozzle cleaning systems and tank agitators can then be used with maximum effect to reduce sludge build up.
Today, Willacy Oil Services has granted exclusivity to Petro-Base Group to operate the SPOT system in eleven countries in Africa and the whole of the United States of America.