Dibutyl Ether and Digestate from a Biogas Plant used in a 3D Plant

Technischer Bericht, 2018

11 Seiten, Note: 1


Table of Contents

Dibutyl Ether and Digestate from a Biogas Plant used in a 3D Plant
1.1 Introduction
1.2 Digestate
1.3 Dibutyl Ether Zero Power Generation
1.4 3D Plant
1.5 Smart System
1.5.1 Smart Soil
1.5.2 Smart Air
1.5.3 Smart Light
1.6 Biomass waste for Dimethyl ether
1.7 Conclusion
1.8 References

Dibutyl Ether and Digestate from a Biogas Plant used in a 3D Plant

Johann Gruber-Schmidt

1.1 Introduction

Biogas Plants are a well-known technology [ 6 ]. Wet substrate is fermented to biogas, a mixture of methane and carbon dioxide. In the most cases biogas is converted with a CHP (combined heat process), in most cases realized with a gas engine, to electricity and heat. Under heat we understand the so called low temperature warm water heat with a temperature range between T=95°C and T=60°C. At the end of the fermentation process we gain the digestate, a mixture of water, solid celluloses and lignin fibers, metals and solved carbonates, potassium oxides, ammonium and phosphate oxides. All these ingredients are well known and used as fertilizers. But the problem is, that fertilizing agricultural land, is not done very day, it is done during the cycle of growing plants before and after seeding to increases the nutrients in the soil. The biogas plant produces much more fertilizer as in normal is needed to support the plants and soil.[ 6, 10 ]

The input substrate for biogas plants roughly can be divided into products of the agriculture like maize including the stems and pips, or sugar sorghum including the stems and pips and waste and manure. Waste and manure are the result of a production process, like straw, or cow manure, horse manure or chicken manure and organic waste from the food industry, hotel sector or restaurants. We focus on the second part the waste and manure. We again gain the digestate at the end of the fermentation process. [ 11 ]

Vertical farming [ 3 ] was an idea raising up about ten years ago. But the idea suffers on the fertilizer costs, the water costs and the housing and cladding costs. In this short report we ask, can vertical farming pushed up to be more productive if we use digestate from a biogas plant, synthetic soil and dimethyl ether as fuel.[ 3 ]

1.2 Digestate

At the end of a fermentation process the most of the biogas has be collected, the depleted substrate of the fermentation process is stored in a tank. This substrate is called digestate. In [ 11 ] measurements show that resting of the substrate for a time range up to 200 days lead to a rest biogas production. The fermentation is a continuous process, therefor digestate is produced continuous. In the most cases digestate is resting in a tank for 200 days and produces up to averaged mean value of ~ 5% biogas. If the tank is open, the biogas is lead to the environment otherwise we have low weak biogas with a caloric heat value Hu ~ 0.5 kWh/m³. Storing in a tank enables to have an influence on fertilizing the agricultural land. But in the most cases there is problem, we gain too much digestate as needed for fertilizing the agricultural land. Both problems, the production of a GHG ( greenhouse gas) biogas and the overproduction of digestate can be solve in preparing, cleaning, separating the digestate from a biogas plant into water, nutrients and slurry.

Table 1: The table shows components of the digestate of a biogas plant operating on waste food and food industry. The components are divided into the group of metals, the group important for fertilizing, the organic part, and the group of pollution. (Source: Johann Gruber-Schmidt, 2018)

As in table [1] described we have three groups of components: we have the organic solids measured under TOC, representing fibers, particles, which can be separated with a sieve on the mechanical way. The next group are the metals, which are also important for the plant. Only the heavy metals like arsenic, cadmium, chrome have to be watched and checked because of the very high toxic potential. The third group are the nutrients needed in a fertilizer, like ammonia, phosphate, potassium, calcium, natrium, in the form of oxides and carbonates and ions. The fourth group is the pollution mentioned under POX (organic fixed halogens), AOX ( absorbed organic Halogens), LAS( solved surfactants), phenols (poly cyclic hydrocarbons ) with high toxic potential.

The mechanical separation process enables to remove the solid particles and is closed with a ultrafiltration process removing particles up to a diameter of 0.1 µm up to 1µm. Ultrafiltration is done with membranes in a pressure range up to 15 bar. The system is back washing with the filtrate solution to reduce the fouling process of the membranes. The filtrate is the first product, consisting of water with metals, carbonates and oxides and solved ions, it is a clear liquid free of particles. This liquid solution can be used for fertilizing plants.[ 1, 2 ]

If we want to enlarge the concentration we use a second membrane process, the well-known nanofiltration operating at a pressure of 30 bar and removing particles with a diameter of 0.001 µm up to 0.1µm. The liquid filtrate has an electric conductivity in the range of 3 up to 5 µS/cm and is often called distilled water or deionized water. The concentrate liquid is not waste it can be stored in tanks and can be used as a high nutrients concentrated fertilizer, stored in a much smaller tank. (approximate ~ 70% of the volume can be saved).

The two-stage process described here in this passage is a solution for plants where high temperature heat is not available. If high temperature heat with a temperature range T=120°C up to T=150°C is available, we can use the process of evaporation of water. This process step leads to a mixture of water and ammonia. All other parts remain in the mud and can only by gained as dry particles (pellets). The pellets cannot be used as fertilizer, they can only be burned in an oven to generate heat. Therefor we will not follow up this way.

1.3 Dibutyl Ether Zero Power Generation

Solid biomass can be converted to synthetic gas, a gas mixture of carbon monoxide, hydrogen and carbon dioxide.[ 13 ] The process is well-known as gasification, in some application used as steam gasification. The synthetic gas is cleaned up, so that we have dust with particles d~ 0.1µm and 0.5 mg/m³ gas, tar with 100 ppm in the gas, oxygen lower than 0.1 vol%, water (steam) lower than 0.5 vol% (dew point lower than – 27°C). The synthetic gas is compressed in two stages up to a pressure of at least 50 bar, more common up to 70 bar. In the first reactor methanol synthesis takes place. Methanol can be dehydrated to dimethyl ether in a second reactor and is a second step. [ 13 ]

Abbildung in dieser Leseprobe nicht enthalten [E1]

Dimethyl ether is the starting liquid to produce dibutyl ether. In the first step we combine hydrogenation and carbonylation to generate ethanol and methanol. From ethanol we generate butanol by dehydration. In the last step we dehydrate butanol to dibutyl ether.

Abbildung in dieser Leseprobe nicht enthalten [E2]

Dibutyl ether can be stored in a tank, is in a liquid phase at environment pressure. The properties of common dibutyl ether are given: ignition temperature 250°C, density 775 up to 820 kg/m³, boiling temperature 140°C up to 250°C, temperature class: T3, heat caloric value Hu= 43 MJ/L (800 kg/m³)) = 10.5 kWh/L, viscosity n = 8.0 mm²/sec ( T= -20°C ).[ 8 ]. Dibutyl ether is a renewable organic fuel. [ 5 ]

illustration not visible in this excerpt

Figure 1: Power Cycle using dibutyl ether generating high temperature heat and the exhaust gas is condensed in carbon dioxide and water. The heat is converted in a cascadic magnetohydrodynamic power cycle generating electricity and heat. [ 4 ] (Source: Johann Gruber-Schmidt, 2018)

Dibutyl ether used as fuel for zero emission power generation is stored in a tank. From the tank it is lead to a swing combustion chamber oxidized to steam and carbon dioxide exhaust gas with high temperature. The heat is converted in a closed cascade magnetohydrodynamic power cycle to electricity and process heat. The power cycle is operating at a high voltage generating direct current (DC). A part if the electric energy is stored in a battery, the electricity is used to provide the electric propulsion engines with electric power. The power range of the module is 500 kWh ele. up to 2000 kWh ele. [ 2 ]

Carbon dioxide and water are stored in separate tanks and will be drained during the filling up of the fuel tanks.

The advantage of the magnetohydrodynamic power cycle, we have no rotating machines like gas turbines or gas engines. The module is small, easy to use and easy to handle and therefor can be applied to drones.

1.4 3D Plant

In our application we are not speaking from vertical farming [ 3 ], we develop vertical farming further to 3D farming. The plant consists of a housing with glass walls to separate the environment from the inner part of the 3D Farm. The structure is made of organic fibers building up the structure carrying the glasses. Inside the farm we have a definite number of floors carrying the basins with synthetic soil. In the middle of the farm the strong light a mixture of solar radiation and synthetic radiation from LED lamps is distributed to the floors. Nutrients and water are distributed by a droplet irrigation, the synthetic air consist of a definite concentration of carbon dioxide, water steam and oxygen. Harvesting is done with a 3D harvesting robot, motion, controlling and 4D flexibility well-known from the 3D printers.

1.5 Smart System

In former times irrigation and fertilizing was done according of nomograms and collected data, depending on the climate and the rain and sun shining periods. The classical farming depends on the strong influence of the environment and the regional climate. In the most cases the irrigation uses too much water (up to 80% more than needed) and the soil structure is not well defined, it depends on the region and the climate, and is a restricting parameter for developing new plants and cultures. [ 9 ]

IT has started to take over the agricultural process years ago and till today it is based on collecting data and trying to make and interpolation into the future. Such systems are not smart and in case they even are no controlling system.

1.5.1 Smart Soil

In the smart 3D Plant we use artificial soil consisting of potassium polyacrylate spheres, foam spheres and wood pellets, sometimes celluloses pellets. The soil enables to store a high amount of water needed by the plant, available at the roots. It gives the plant stability and it is easy to penetrated by the roots. Because of the storage of water in the potassium polyacrylate spheres, the irrigation can be reduced up to 80%. The water is stored in the spheres. If we us the nutrient fertilizers from the digestate of the biogas plant, we can reduce the synthetic fertilizing about 80%. [ 10 ]

1.5.2 Smart Air

In the smart 3D Plant we use artificial air, consisting of carbon dioxide, oxygen and steam. Oxygen is needed in the dark cycle producing glycoses form carbon dioxide. The air is heated up to a temperature T=35°C and heats up the 3D plant housing. The carbon dioxide needed from the plant depends on the light intensity and the water availability (ions) at the roots. [ 9, 10 ]

1.5.3 Smart Light

In the smart 3D Plant we use the common classical solar radiation as provided by the climate depending on the local region. To increase the conversion of carbon dioxide we need a higher light intensity often called strong light. Measurements [12] have shown that we can apply the following relations:


1 ml/l CO2 concentration in the artificial air ó 20 000 Lx (strong light) ó 100 W/m²

5 ml/l CO2 concentration in the artificial air ó 100 000 Lx (strong light) ó 500 W/m²

The synthetic artificial light has a wave length range 480 nm up to 720 nm. In this wave length range the maximum on oxygen production can be achieved. Measuring of oxygen enables to control the carbon dioxide conversion process.


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Dibutyl Ether and Digestate from a Biogas Plant used in a 3D Plant
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dibutyl, ether, digestate, biogas, plant
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Dr. techn. Johann Gruber-Schmidt (Autor:in), 2018, Dibutyl Ether and Digestate from a Biogas Plant used in a 3D Plant, München, GRIN Verlag, https://www.grin.com/document/435053


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