Sludge blockages can cause a reduction in biogas output, which can be cured using an inline Mono Muncher for its tearing, shearing and crushing action. If your biogas yield drops unexpectedly, it could be due to a problem with your digester's sludge homogeneity.
It's possible that your system isn't mixing efficiently, and if your internal or external mixer flow rates are lower than you'd like the sludge may need homogenizing by shredding it in situ.
A variety of factors could be to blame for these digester gas output issues, but one to keep an eye out for is a full or partial blockage of your digester slurry pipe used for recirculation. If so consider adding a Mono Muncher in-line shredder to the digester tank to cut reduce the particle size and lower the viscosity.
The obstruction of the flow within the pipe caused by a buildup of digester substrate slurry is referred to as sludge blockage. Sludge blockage occurs when a combination of organic slurry and sediment, such as sand, grit, and stones, plus plastics, accumulates in the invert of the mixer recirculation pipe, reducing the effective cross-sectional area and increasing friction losses.
A partial or full blockage results in a lower flow rate, which reduces output from mixer jets, and that means the loss of biogas revenue. Additionally, an unresolved blockage can cause impeller cavitation, which can lead to pump damage.
What is the best way to avoid a sludge blockage in a mixer pipe?
The installation of a Mono Muncher from Fluid Motion Solutions’ (part of NOV Inc) is our solution for reducing sludge viscosity and preventing this type of sludge blockage.
Press Release 11 August 2022:
Mono Muncher sends biogas yields up in Spain
The installation of a Fluid Motion Solutions’ (part of NOV Inc) Mono Muncher at a biogas plant in Spain has helped increase gas yields by 8%.
Designed for the homogenization of sludge in digestion, feeding and recirculation, the inline Mono Muncher’s tearing, shearing and crushing action has removed a bottleneck in the system that was causing blockages, and downtime with significantly extra maintenance.
Supplied with a custom-designed control system, the 180 m3/hour flowrate shredder has a proven track record of protecting pumps from blocking by fine-grinding AD feedstocks such as municipal sludge and food waste.
In the event of an object initially being too strong, the Mono Muncher’s overload protection technology reverses the cutters (to clear the cutter stack), with any solids falling into the trash trap.
The Mono Muncher can also be utilised in a wide variety of industrial applications where solids such as plastics, clothing and bones need to be reduced in size. These include mud-contaminated drill cuttings, aircraft sewage, abattoir waste, and wastewater from prisons.
Fluid Motion Solutions, Greengate, Middleton, Manchester, England M24 1SA
+44 (0) 161 339 9000
PR Ends
Sludge Pump Blockages
This unit operates to reduce the particle size of the solids in the digester and pipework. These units are ideal for a biogas plant that suffers from clogging up when the fibrous materials in the substrate interlock together and form a plug, restricting or stopping, the flow in the pipe.
A welcome spin-off effect is an increased biogas yield from the same feed. This occurs due to the manner in which the unit increases the digestibility of the solids by raising the surface area from which the methanogenic microorganisms can attack and eat the cells, grow and make the mostly methane biogas.
In one mixer system design, a sludge homogenizing device has a pair of vertically extending suction lines, each of which alternately provides suction and discharge of the sludge. This arrangement may also include a pump that agitates the sludge, and/or one or more pumps that alternately provide suction and discharge of the sludge.
Sludge is by nature a mixture of water and a solid that can be a sticky substance. It is a byproduct of many processes and industries, and at best it behaves like a thick, viscous fluid. Experts divide sludge into two different types: settling and non-settling. The former is more stable and wears down less easily. Hence, it is important to know which type of sludge is present for its effective homogenisation.
Another application of this sludge treatment process, in addition to the anaerobic digestion industry, is in the wastewater industry. Thickened sludge, containing between 8% and 11% dry matter, presents a challenging handling problem in any application, as it no longer has linear flow characteristics similar to water.
An alternative option of progressing cavity pumps is an expensive solution used at times and can be high-maintenance in high abrasion tank bottom gritty sludges. They are pumps which have generally been designed to ensure consistent conveying of less abrasive sludges than these. They are installed at the appropriate locations in the process and work reliably to move a density of solids that would cause blockage in other systems. That would seriously reduce bacterial activity. However, where a Mono Muncher can be used, to homogenize the sludge to keep it moving, it can be a lower-cost option.
The composition of digester sludge varies, and its characteristics are influenced by the feed material. The chemical composition of the sludge is also highly dependent on the feedstock, the presence or not of contaminant materials, and their nature. Nonetheless, sludge homogenization can be an effective method of avoiding blockages.
High-pressure homogenization (HPH) involves 30 to 150 MPa pressure. It is a form of thermal treatment that involves impacting sludge. The effect is to break up cell membranes and disrupt the cellular structure. In addition, HPH can lead to maceration and electroporation. In a study by Kopplow and Barjebruch, sludge treated with HPH at 600 bars was found to have 25% lower volatile solids than before treatment. However. this is not usually suitable for digester applications.
Microwave pre-treatment may raise gas yield by the opening of the cell walls of otherwise tough-to-digest organic matter. And, while it may be an advanced version of AD pretreatment and is an effective method for reducing volatile solids. Microwave irradiation will not help to increase the efficiency of mixing and mobilising heavy sludge at the bottom of the digester although it can reduce sludge formation in the digester overall.
