Improve Effectiveness with Mobile Solution
Almost 60 NEUMAN & ESSER (NEA) compressors are running in German biogas plants of varying sizes and feed the purified biomethane into the existing natural gas grid. Depending on the grid, the NEA compressors have to increase the gas pressure of 0 to 9 bar(g) to up to 84 bar(g). Local different grid pressures even exist for the same grid operator.
24 biogas compressors are in operation for the company Ontras Gastransport. Biogas is an important issue for the transmission grid operator headquartered in Leipzig. Ontras is involved in national and international committees, helping to design the future framework conditions. However, also the large operators are subject to the changes in subsidy policy and looking for opportunities for long-term investment security within the biogas market.
Continuous changes to the market demand the most efficient production concept. Interim processes move into focus. These periods which have to-date remained unused, possess the potential to improve the overall degree of effectiveness decisively. Therefore, Ontras looked for a mobile biomethane compressor solution in order to feed the gas into the gas grid early, even before the stationary compressor system is commissioned.
MoBIO 800 ready for use within one day
The mobile biogas compressor is designed to handle the appropriate gas pressures and feed rates for all of the Ontras biogas systems. Also, in case of a failure or malfunction in a stationary system, it should be possible to connect and use the mobile solution in the short-term. Ontras has had good experience with its long-term partner NEUMAN & ESSER and therefore decided in favor of NEA’s convincing concept. As a result, planning commenced at NEA in Wurzen in 2014.
One year later, the turnkey solution stands on the Wurzen factory premises. Ontras’ Project Manager Jens Geier was impressed: “We were amazed to be able to marvel at the MoBIO 800 on the NEA grounds after a mere twelve months. Fully completed and ready to go, including the permission to drive on the road.”
The mobile system consists of two trailers. The split was made due to the requirement to develop one system for all cases of operation within the Ontras gas grid as well as to enable assembly, servicing, cable, escape and rescue routes. As for all NEA compressors, this mobile system is also designed for low maintenance continuous operation.
Two dry running gas-tight NEA reciprocating compressors, driven by a 315 kW mid-mounted engine, are located in the first trailer. The second trailer houses the water coolant and container air-conditioning, steering, controlling as well as the control air generation. Moreover, extensive accessories such as supports, landing gear, lightning protection rods, oil and glycol vessels, concrete weights, load plates and further outdoor assembly parts are housed there during transport. Additionally, the mobile biogas system can be remotely monitored. All safety-relevant aspects such as fire notifications, gas leaks or break-ins can be recorded at the Ontras headquarters in Leipzig, as can the complete technical data.
The second trailer is considerably lighter than the first; the axles and double supports are sufficient to set it up. Its heavy brother is fully supported by existing supports as well as additional extension supports during operation and is therefore independent of the chassis. Flexible connectors between the trailers enable commissioning within one day.
The mobile compressor system achieves a gas production volume of at least 800 Nm³/h for all the different and specified pressure conditions. The suction pressures fluctuate between 1 and 10 bar absolute dependent on biogas generation like amine gas treating or PSA. The final pressures lie within the range from 16 to 85 bar (absolute) – depending on the use location and case as well as the attached gas grid.
Principally, NEA distinguishes between two-stage and three-stage feeding as well as recirculation for the possible applications. Due to the different pressures, the different modes of operation for this mobile system are adapted by efficient, energy-saving regulation (rotational speed and bypass regulation) as well as by disconnecting a reciprocating compressor.
Combined strengths for high-performance application
Even if it sounds so simple, it was an incredible act of strength in reality Axel Korschewski, Plant Engineering Manager at NEUMAN & ESSER in Wurzen explains: “We bundled our experience and resources for MoBIO. Otherwise we couldn’t have handled it. However, we have also recognized what we are capable of. A large number of ideas flowed in, which had not yet happened in this manner. We had to fully take on new paths and establish several new questions that arose when solving the problem. Therefore, complex thoughts which intervened in several areas, were required in order to avoid getting onto the wrong track.”
The greatest challenge was to achieve the necessary rigidity of the trailers while taking the maximum permissible overall trailer weight into account. As Project Manager Philipp Leipner explains: “The couplings have a maximum tolerance of only 0.2 mm in order to operate the system with the accustomed NEA precision and performance efficiency. Therefore, also the base frame is hardly allowed to move – at the most 1 mm over the full length of 9 m. Torsional movements of 5 cm and more are normal for common trailers.“ Consequently, the rigidity of the chassis had to be increased by a factor of more than 50 without losing sight of the weight.
It was agreed in the performance specifications that the mobile compressor system must be appropriate for normal road traffic without a special permit – for a standard truck so that the system is at the use location fast, i.e. dimensions, weight, etc. must be in accordance with the highway code. So the compressor solution had to be light and rigid enough. Additionally, transport should be possible when full (water-glycol mix as well as oil system filling), making it possible for the system to be connected and commissioned as fast as possible.
The initial idea to construct the compressor based on NEA SAPS (Seismic Air Power System) was abandoned fast. The combination of a screw compressor and a reciprocating compressor would have exceeded the maximum permissible weight by at least 10t.
The maximum permissible overall weight for a tractor and trailer in Germany is 40t. “It became apparent to us very quickly that we would have to completely rethink the mobile compressor and create an entirely new construction”, as Axel Korschewski describes the outset of the project.
“The first task was to determine the space requirements precisely”, explains Philipp Leipner. “The questions were: Where must the service technicians for servicing work later go, how much space do they need for controlling and how much for servicing lines and connections? Then, we had to take the exchange of valves and, if applicable, of a cylinder into account. As it were, we had to piece a jigsaw together while repeatedly calculating and checking the strengths and torsional forces.” Also, the engineers had to take the environmental guidelines (e.g. Water Resources Law), work protection, fire protection, escape routes and the operator Ontras’ specifications into consideration.
A rigid steel frame was designed within the course of planning, doing justice to the requirements regarding the overall weight. Access is provided to all the wear parts for servicing work. Even some of the roof elements can be removed easily, enabling access to the corresponding points from above and, as necessary, exchange of the cylinders within the shortest of time. The system has various steps and stages, enabling easy access to all connectors and fitting positions.
Operation is guaranteed at outdoor temperatures between -20° and +35°C. “Noise protection and air-conditioning technology are contradictory in-part“, as Korschewski interjects. “Above all against the backdrop, we constantly have to pay attention to the weight. The hinges and door locks alone weigh 300 kg.” The NEA engineers were repeatedly confronted with extreme opposites for which they had to find the ideal solution. In addition to noise, “rigid but light” as well as “compactness with full access” posed the greatest challenges.
Several opportunities for the future
Everybody involved in this project learned a great deal and outgrew themselves. Philipp Leipner summarizes: “The limits lie in the weight and construction space. At the cost of the short development time, we were not yet able to exhaust all options. From the kick-off meeting to delivery, we had a mere eleven months’ time. However, we have already recognized optimization ideas and weight reduction potential here and there.”
The Plant Engineering Manager also sees potential: “We know how it works now. A fully-fledged system which can also be operated permanently exists and is not more expensive than a stationary system. The carry-over effect has transpired as particularly interesting. In principle, we are able to put any compression process desired onto the trailer, providing us with an unlimited application portfolio. For example, this could be a complete functional unit for a chemical process. If a compressor at a chemicals works fails, we can also design this compressor technology in mobile form.”
Several further applications options are conceivable, for example for chemically identical natural gas as a backup system or for feeding into the gas grid, also making these processes flexible. The mobile systems can also recirculate or force off. Although the system in its current status is “overqualified” for this, it is one of the further application options for this system.