MoBiDic: Tailor-Made Transfer Pumping of Natural Gas Instead of Blowing It Out - Protects the Environment and Avoids Gas Losses

by Emilia Haep and Dr. Ralf Borschinsky (ONTRAS)
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MoBiDic: Tailor-Made Transfer Pumping of Natural Gas Instead of Blowing It Out - Protects the Environment and Avoids Gas Losses

In the discussion about greenhouse gas emission savings, methane emissions, after CO2 emissions, account for the largest percentage of all GHG emissions in Europe. Methane emissions come from various sectors of the economy, including the natural gas industry. Therefore, when considering the potential for savings, the natural gas network also plays a significant role in the challenge of addressing climate change. 

ONTRAS Gastransport GmbH (ONTRAS) is a transmission system operator for natural gas based in Leipzig, Germany. With around 7,700 km of pipeline, it operates Germany's second-largest long-distance pipeline network. Avoiding methane emissions from gas losses during planned work on natural gas pipelines has been a central concern of ONTRAS for many years.

When repair work is carried out on the natural gas network, the affected section of the pipeline must first be evacuated of gas. In the past, blowing out residual gas into the atmosphere was a common and accepted method for this purpose. This entailed two decisive disadvantages. Considerable amounts of methane were released into the atmosphere, resulting in correspondingly high gas losses and thus financial losses for the gas network operator. Therefore, ONTRAS looked for alternatives at an early stage to avoid the blowout. If a second pipeline with correspondingly available absorption capacity was available, ONTRAS resorted to service providers to pump the gas volumes to be expanded into the second pipeline section using a mobile compressor.

However, only limited mobile compressors services are available for this throughout Europe. Often, these compressors do not have the necessary technical requirements by the ONTRAS network and the availability for planned operations - especially for short-term appointments - often turned out to be difficult. In addition, the planning, tendering and awarding of contracts required in each case was very time-consuming for the service providers. After a detailed evaluation of all options, ONTRAS initially decided to use its own mobile compressor to ensure more flexibility. To reduce methane emissions, the existing mobile compressor – NEUMAN & ESSER MoBIO 800 - was used.

Temporary Solution: Evacuating With MoBIO 800

The MoBIO 800 has already been part of the ONTRAS fleet since 2014 and originally had a different application purpose. In order to ensure the legally required high availability of the 23 biogas feed-in plants on the ONTRAS network, ONTRAS had designed the MoBIO 800 - a mobile compressor unit with two V-compressors driven by a 315 kW double-ended motor - together with NEUMAN & ESSER in order to be able to quickly set up a replacement solution in the event of a feed-in failure. Accordingly, the MoBIO800 was built universally, but also specifically for the needs of these biogas plants.

The MoBIO 800 offered the great advantage that it was already available as a mobile solution and could be used directly for pumping. Since the MoBIO 800 was originally designed for a different application, it could not quite meet the increased requirements for pumping over. These included the significantly increased pumping capacity and the flexibility of a permanently deployable mobile solution, without the need for additional commissioning tests prior to use. Thus, the need arose for a new, more powerful mobile solution that could be set up and dismantled quickly and was optimized for the ONTRAS pipeline network.

The Birth of the MoBiDic

Based on the experience with the MoBIO 800, the ONTRAS engineers defined the requirements for the new plant in 2019: The machine was to run autonomously and be mounted on only one full-size trailer. In addition, it should be possible to set it up on any flat, load-bearing surface without additional effort. The maximum possible pumping volume flow was to be achieved for a main pressure range of 16 bar to 40 bar, and the pressure of the pipeline section to be emptied was to be reduced as much as possible in the process.

ONTRAS awarded the engineering contract based on the very good experience gained in previous projects and the binding assurance that the maximum possible delivery volume could be achieved with single a mobile evacuation compressor from NEUMAN & ESSER. During the project period of about two years for the engineering and the actual construction of the plant, there was intensive cooperation between NEUMAN & ESSER and ONTRAS. Already during the project phase, ONTRAS was able to follow the respective intermediate status of the plant. Using the AutoCAD Plant 3D software, the plant could be visualized as a 3D model. ONTRAS was also given the opportunity to virtually inspect the mobile pipeline evacuation compressor with VR glasses. The ease of maintenance and accessibility of individual components could thus be checked live - even before the start of construction. This resulted in a planning work that was precisely tailored to ONTRAS and its network conditions. The construction of the transfer compressor at NEUMAN & ESSER then started on this basis.

NEUMAN & ESSER stands for customer-specific solutions under particularly demanding conditions. Therefore, with focus on the maximum possible flow rate, the mobile pipeline evacuation compressor was developed, which could not be found on the market with this performance so far. This solution from NEUMAN & ESSER is mounted on only one trailer and driven by a gas engine of 770 kW. All system components, such as the water cooling, air conditioning, control, regulation and the accessories for the superstructure are installed on the trailer. An innovative design for maximum delivery volume in minimum space with adequate maintenance friendliness.

In order to keep ONTRAS' time expenditures, downtime costs and emissions as low as possible, a particularly high pumping capacity is indispensable. Due to the special compressor design, geared to the maximum delivery volume, a gas-tight compressor type 2TVL63 GTC (2-stage, dry-running, 4-crank, horizontal) compresses up to 68,000 Nm³/h of natural gas up to 45 bar(g) discharge pressure into another gas pipeline. The 2TVL63 GTC was designed with a particularly short engine and a special cylinder construction rotated by 45° to make maximum use of the given space of the trailer. The gas-tight design of the crankcase prevents gas emissions even during the evacuation process.

In order to allow short-term operations and to avoid permit waiting times, the mobile unit was built according to the STVZO relevant standard external dimensions. Due to the special design regarding weight distribution, a non-route-related permanent exemption has been achieved. By means of various auxiliary systems and a complete control cabinet unit, this plant enables self-sufficient operation, as the plant is operated via the natural gas available in long-distance pipelines at the respective location. The set-up time from delivery to commissioning of the mobile compressor unit is only about two hours.

After successful completion and acceptance by the TÜV, the trailer was given its final visual polish and its name "MoBiDic", which was the clear winner of the internal ideas competition at ONTRAS. Then came a three-week trial run. In Milzau, Germany, in the West network area, NEUMAN & ESSER, together with Streicher Anlagenbau, various specialist companies and ONTRAS, simulated typical pumping conditions and carried out several endurance tests.

The test phase showed that each new use of the MoBiDic also brings new conditions. It is particularly noteworthy that during the test phase the promised maximum flow rate of 68,000 Nm³/h was clearly exceeded. The first successful pumping operation then took place in Maukendorf, Germany.

This was followed by further operations in the German locations Leuna, Großenhain, Bobbau, Brusendorf and Lauchhammer. Each new operation brought new insights and led to further technical optimizations, which the engineering team was able to implement within a very short time until the next operation.

The track record of the first year: 1,450,000 Nm³ of natural gas were pumped, which would otherwise have been released into the atmosphere. The amount of gas saved can supply around 650 single-family homes for a year. In total, emissions equivalent to around 28,000 metric tons of CO2 were avoided, equivalent to 280 million passenger car kilometers.

During the turn of the year 2021/2022, the first annual and conservation maintenance of the MoBiDic took place at the NEUMAN & ESSER site in Wurzen. Also, the expectations with regard to lower wear were met during this period. The compressor set out at the beginning of 2022 to again avoid emissions during repair work. The ONTRAS repumping program already promises a full schedule for the support team and the MoBiDic.

The successful cooperation between NEUMAN & ESSER and ONTRAS has already made a significant contribution to environmental protection. The green visions of both companies are united in their determination to continue saving the maximum amount of methane emissions in the future.

Features of the Mobile Compressor:

  • Increased Volume: 68.000 Nm3/h
  • Suction pressure: 2 - 45 bar (g)
  • Discharge pressure: 7 - 45 bar (g)
  • Gas engine power: 770 kW/span>
  • Gas-tight engine
  • Total weight: approx. 40 t
  • Dimensions: 13,00 m x 2,55 m x 2,70 m