IMPLEMENTATION OF THE MPB.
AGF has been updating and reporting in various blog posts the development of the decentralised waste management and biogas production project through the creation of a commercial product, the MPB. The whole development of this MPB Mini Biogas Plant and the initial planning of the project has been affected by COVID 19 and its consequences. What was planned for the end of March could not be completed until June. This mean that the initial plan had to be modified and the plant was commissioned and tested during the month of June. At the beginning of this month, the assembly of the MPB plant in the workshop was completed and it was sent to the BIOGASNALIA biogas plant in the Villalonquéjar industrial park, in Burgos, for commissioning and testing.
Once it is located at its destination, the AGF team proceded to certify the operability of the installation and to install the control programme, the plant was commissioned until it was fully operational and ready for the first load. The MPB plant has the same capabilities and processes as an industrial plant with the design and technology of AGF. This makes it a complex system to start up and operate, independently of its size and reaction volumes. Building an industrial plant to such a small scale without losing functionality is a complicated task, and requires a considerable time for long-term testing to ensure that it has been fully achieved.
The plant was loaded with activated sludge from the biogas plant, the biogas generated could be consumed for the start-up of the entire heating system. Therefore, no external energy source was necessary for this start-up. The electricity consumption of the MPB is taken from the production of the industrial biogas plant, which keeps the plot in a total energy island, electrical and thermal. This MPB model does not have any electricity production equipment installed, although it is prepared for installation in the future if is considered appropriated.
Since this inoculum filling, the MPB has been producing gas for the last two weeks and has been fed with organic waste collected from different partners. The waste was collected from different companies, hotels, bars and restaurants in order to simulate the normal feeding of the plant. This waste, after prior separation, was fed to the plant, which processed it according to the control programme.
The aim of this collection was also to quantify the amount of organic waste available, its quality and its degree of separation at source. During this collection, it was possible to feed a mixture of organic matter with a high potential for biogas production.
These feed loads have been used to test and evaluate the entire organic waste feed system of the plant, which has processed hundreds of kilorgams of biodegradable waste of all kinds per day and has been converted to biogas.
After these weeks of launch and operation, it can be announced that the plant has achieved the following objectives.
- Control of biogas production. The plant has been producing biogas in a controlled way, without any kind of gas storage. Three different control strategies for this on-demand production process have been sucessfully tested, each appropriate for different plant operations and gas uses. The gas flow rate of the plant has been constant at the desired value has been installed in the MPB.
- Automatic operation of the plant. The plant has operated for a week with all the main functions of the plant in automatic mode, which is a demostration of the operation of this plant and has allowed us to evaluate the real need for manpower in this installation.
- Relative production similar to or higher than the insutrial plant. The MPB has produced with an average volumetric efficiency (Nmb3mR-3·d-1) similar to the industrial plant, being at times above this production efficiency. This is a proof of the promising future that reverse scaling of AGF technology can have.
- Temperature control. The plant is able to maintain a high level of control over process temperatures, with a heating design similar to an industrial plant of AGF. This is a serious problem in industrial plants, where there is no effective control of temperatures and strong termal gradients within the large reaction volumes.
- Self consumption of biogas. All the biogas generated has been consumed in the safety flare of the plant, except for the gas required in the boiler to maintain process temperatures, which has been a small fraction of the total produced. In this unit there is no end use of the biogas at the moment, reason why it has been flared.
The MPB plant has been designed to be an autonomous installation with the purpose of process waste without the need of any other element. From a gas point of view, it can be used to produce electricity and/or heat, with biomethane production being the biggest possible challenge on a small scale.
To meet this challenge, AGF has designed a gas separation plant for low cost biomethane production.
ENRICHMENT PLANT TESTS.
The MPB has been designed by integrating a low pressure enrichment plant, the MP2B. The idea is to use this plant when the potential use of the gas requires the generation of biomethane, and will depend on each project. Therefore, a Mini Biogas Plant (MPB) that integrates the enrichment process called MPB2 (Mini Biogas and Biomethane Plant) regardless of the end use of the gas.
If the MPB must be commercially affordable and profitable, the MP2B must also satisfy these requierements, so that the enrichment plant must not involve a large investment and, above all, operating cost. For this reason, no type of enrichment requiring high gas pressure has been considered suitable and the enrichment plant has been designed for optimum separation by water solubility of the gases working at low pressure.
It is a new process that works with the MPB. The plan control is complex, reaching systems that would be difficult to be regulated by controlers PID in transitory response, and that requires the tune of compensators for its great snowball effect. Finally, the first version of the control system has been installed, which has been used to test the enrichment plant using the constant gas flow rate of the MPB plant.
The enrichment plant has been tested for days processing a constant flow of biogas generated in the MPB. The picture above shows the effect of the enrichment plant on the flow rates of the plant, the blue line measurement being the flow rate reading of the biomethane generated in the enrichment plant, the orange line is the biogas produced by the MPB plant.
Therefore, its efficiency as a gas separation process has been evaluated. Different valid operating points have been reached, and it has been possible to obtain a gas with a methane content of more than 90% in mole fraction. The most stable gas obtained had a composition as shown, keeping these values practically constant for hours. The maximum methane content obtained was 95%, which is a very promising result, as it is a first approximation to the operation of this plant and is available for the optimisation of the process.
In the MP2B plant, the gas produced – whether biogas or biomethane – has been used to produce hot water for the own consumption of the plant. The rest of the biogas has been sent to the flare, where the variation in the richness of the gas burned can be visually verified, being the combustion of the enriched gas close to the combustion of natural gas.
More experience will be needed in the long term to make this plant a commercial product, but the expectations are promising. It is a first step on the road to a commercial product that can make decentralised waste management and renewable gas production profitable and possible.
This is one of the great challenges facing the biogas industry, and AGF is determined to make its contribution as a developer of new products based on proprietary processes.