Hybridizing concentrated solar power (CSP) with biogas and biomethane as an alternative to natural gas: Analysis of environmental performance using LCA

Concentrating Solar Power (CSP) plants typically incorporate one or various auxiliary boilers operating in parallel to the solar field to facilitate start up operations, provide system stability, avoid freezing of heat transfer fluid (HTF) and increase generation capacity. The environmental performance of these plants is highly influenced by the energy input and the type of auxiliary fuel, which in most cases is natural gas (NG). Replacing the NG with biogas or biomethane (BM) in commercial CSP installations is being considered as a means to produce electricity that is fully renewable and free from fossil inputs. Despite their renewable nature, the use of these biofuels also generates environmental impacts that need to be adequately identified and quantified. This paper investigates the environmental performance of a commercial wet-cooled parabolic trough 50 MWe CSP plant in Spain operating according to two strategies: solar-only, with minimum technically viable energy non-solar contribution; and hybrid operation, where 12 % of the electricity derives from auxiliary fuels (as permitted by Spanish legislation). The analysis was based on standard Life Cycle Assessment (LCA) methodology (ISO 14040-14040). The technical viability and the environmental profile of operating the CSP plant with different auxiliary fuels was evaluated, including: NG; biogas from an adjacent plant; and BM withdrawn from the gas network. The effect of using different substrates (biowaste, sewage sludge, grass and a mix of biowaste with animal manure) for the production of the biofuels was also investigated. The results showed that NG is responsible for most of the environmental damage associated with the operation of the plant in hybrid mode. Replacing NG with biogas resulted in a significant improvement of the environmental performance of the installation, primarily due to reduced impact in the following categories: natural land transformation, depletion of fossil resources, and climate change. However, despite the renewable nature of the biofuels, other environmental categories like human toxicity, eutrophication, acidification and marine ecotoxicity scored higher when using biogas and BM

Granular activated carbons from avocado seeds

Avocado seeds have proven to be an excellent raw material for the production of Granular Activated Carbons (GAC). This residue, generated in large amounts in centralized facilities dedicated to the transformation of avocado fruit, has no commercial value at present. GAC have been produced by partial gasification of ground seeds under mildly oxidizing conditions (steam/nitrogen mixture). Optimum activation conditions were achieved at 1000 ºC and residence times between 120-150 min, resulting in burn off rates between 34-37 wt% and carbon yields between 12.4-13.0 wt%. These GAC exhibited type IV N2 gas adsorption isotherm, characteristic of materials containing a mixture of micro and mesopores. Avocado seed GACs exhibited BET surface areas up to 700 m2 /g, CO2 surface areas up to 900 m 2 /g and micro-pore volumes up to 0.31 cm3 /g. This porous structure provided these GAC with a remarkable aqueous adsorption capacity for methylene blue (Langmuir qm = 153.8 mg/g and Freundlich Kf = 113.0 mg/g), which was greater than that determined for a range of GAC commercialized for the treatment of waste and drinking waters

Life cycle assessment of concentrated solar power (CSP) and the influence of hybridising with natural gas

Purpose Concentrating Solar Power (CSP) plants based on parabolic troughs utilize auxiliary fuels (usually natural gas) to facilitate start-up operations, avoid freezing of HTF and increase power output. This practice has a significant effect on the environmental performance of the technology. The aim of this paper is to quantify the sustainability of CSP and to analyse how this is affected by hybridisation with different natural gas (NG) inputs. Methods A complete Life Cycle (LC) inventory was gathered for a commercial wet-cooled 50 MWe CSP plant based on parabolic troughs. A sensitivity analysis was conducted to evaluate the environmental performance of the plant operating with different NG inputs (between 0 and 35% of gross electricity generation). ReCiPe Europe (H) was used as LCA methodology. CML 2 baseline 2000 World and ReCiPe Europe E were used for comparative purposes. Cumulative Energy Demands (CED) and Energy Payback Times (EPT) were also determined for each scenario. Results and discussion Operation of CSP using solar energy only produced the following environmental profile: climate change 26.6 kg CO2 eq/KWh, human toxicity 13.1 kg 1,4-DB eq/KWh, marine ecotoxicity 276 g 1,4-DB eq/KWh, natural land transformation 0.005 m2/KWh, eutrophication 10.1 g P eq/KWh, acidification 166 g SO2 eq/KWh. Most of these impacts are associated with extraction of raw materials and manufacturing of plant components. The utilization NG transformed the environmental profile of the technology, placing increasing weight on impacts related to its operation and maintenance. Significantly higher impacts were observed on categories like climate change (311 kg CO2 eq/MWh when using 35 % NG), natural land transformation, terrestrial acidification and fossil depletion. Despite its fossil nature, the use of NG had a beneficial effect on other impact categories (human and marine toxicity, freshwater eutrophication and natural land transformation) due to the higher electricity output achieved. The overall environmental performance of CSP significantly deteriorated with the use of NG (single score 3.52 pt in solar only operation compared to 36.1 pt when using 35 % NG). Other sustainability parameters like EPT and CED also increased substantially as a result of higher NG inputs. Quasilinear second-degree polynomial relationships were calculated between various environmental performance parameters and NG contributions. Conclusions Energy input from auxiliary NG determines the environmental profile of the CSP plant. Aggregated analysis shows a deleterious effect on the overall environmental performance of the technology as a result of NG utilization. This is due primarily to higher impacts on environmental categories like climate change, natural land transformation, fossil fuel depletion and terrestrial acidification. NG may be used in a more sustainable and cost-effective manner in combined cycle power plants, which achieve higher energy conversion efficiencies

Environmental Assessment of a HYSOL CSP Plant Compared to a Conventional Tower CSP Plant

The aim of this paper is to evaluate the environmental performance of a Concentrating Solar Power (CSP) plant based on HYSOL technology. The plant under investigation is a solar tower system with 14 hours thermal energy storage using biomethane as auxiliary fuel and using a 100 MWe steam turbine and a 80 MWe gas turbine in the combined cycle (Brayton and Rankine) characteristic of the HYSOL technology. The results evidence that HYSOL technology performs significantly better in environmental terms than conventional CSP. This evidence is particularly relevant in the climate change category where HYSOL plants presents 43.0 kg CO2 eq /MWh. In contrast, the hybrid CSP plant operating with natural gas emits 370 kg CO2 eq /MWh. This difference is attributable primarily to the nature of the auxiliary fuel (biomethane in HYSOL and natural gas in conventional CSP), but also to the higher thermal efficiencies achieved in the HYSOL configuration, which prevents the emission of 106 kg CO2 eq /MWh. The environmental significance of the additional components and infrastructure associated with the Brayton cycle in the HYSOL technology (gas turbine, Heat Recovery System and Low Temperature Energy Storage) are negligible

Biomass Gasification in a Fluidized Bed Reactor: Effect of Temperature, Stoichiometric Ratio and Biomass Type

This paper investigates the gasification of two biomass types (pine wood and olive stones) in a laboratory scale bubbling fluidized bed reactor, in order to evaluate comparatively their potential in the production of syngas

Socio-economic effects of a HYSOL CSP plant located in different countries: An input output analysis

The aim of this paper is to estimate the socioeconomic effects associated with the production of electricity by a CSP plant with HYSOL configuration, using Input Output Analysis. These effects have been estimated in terms of production of Goods and Services (G&S), multiplier effect, value added, contribution to GDP, employment creation and labor intensity. The analysis has been performed considering that the plant was established in four countries contemplated as suitable for HYSOL technology: Spain, Mexico, Chile and Kingdom of Saudi Arabia. The results indicate that producing electricity in a HYSOL CSP plant generates positive impacts on the economy and the employment in every country, producing the following ranges of socio-economic effects: a 0.05%-0.38% increment of the national GDP, creation of 11662-21053 jobs-year and production of 1412-2565 M$ of domestic G&S. The economic results are particularly favorable for Spain and Chile, which has been associated with higher multiplier effects (2.05 and 2.01 respectively) and higher demand of G&S in the Operation and Maintenance phase. In the case of Chile, favorable results are also due to the national production of nitrate salts employed in the thermal energy storage system. Employment results are more favorable in Mexico and Chile, which has been associated with the higher labor intensity of its national economies

LCA of alternative biochar production technologies

This paper investigates the environmental performance of biochar produced using different technologies including: traditional earth kiln; metal ring kiln, Missouri kiln and Missouri with gas recycling. The analysis has been produced using Life Cycle Analysis (LCA) and includes extensive inventory of direct gas emissions during the carbonization stage. The normalized analysis evidence that the impact categories most severely affected are photochemical oxidant formation, human toxicity and climate change. In the case of climate change, impact values ranged between 2773 and 4714 kg CO2/ton, with lower emissions produced by advanced carbonization technologies due to higher product yields, improved thermal efficiency (which results in reduced combustion of primary products) and elimination of volatile pollutants in the gas condenser and post-combustor. Single point indicator analysis evidences a 33-40 % reduction in environmental impact when using advanced processing methods compared to traditional charcoal production

Environmental analysis of a Concentrated Solar Power (CSP) plant hybridised with different fossil and renewable fuels

The environmental performance of a 50 MW parabolic trough Concentrated Solar Power (CSP) plant hybridised with different fuels was determined using a Life Cycle Assessment methodology. Six different scenarios were investigated, half of which involved hybridisation with fossil fuels (natural gas, coal and fuel oil), and the other three involved hybridisation with renewable fuels (wheat straw, wood pellets and biogas). Each scenario was compared to a solar-only operation. Nine different environmental categories as well as the Cumulative Energy Demand and the Energy Payback Time (EPT) were evaluated using Simapro software for 1 MWh of electricity produced. The results indicate a worse environmental performance for a CSP plant producing 12% of the electricity from fuel than in a solar-only operation for every indicator, except for the eutrophication and toxicity categories, whose results for the natural gas scenario are slightly better. In the climate change category, the results ranged between 26.9 and 187 kg CO2 eq/MWh, where a solar-only operation had the best results and coal hybridisation had the worst. Considering a weighted single score indicator, the environmental impact of the renewable fuels scenarios is approximately half of those considered in fossil fuels, with the straw scenario showing the best results, and the coal scenario the worstones. EPT for solar-only mode is 1.44 years, while hybridisation scenarios EPT vary in a range of 1.72 -1.83 years for straw and pellets respectively. The fuels with more embodied energy are biomethane and wood pellets

Base Case Analysis of a HYSOL Power Plant

Concentrating solar power (CSP) plants are regarded as an alternative solution for electricity generation. The main drawback of this technology is related to the intermittent and seasonal nature of the solar irradiation. As a consequence, most CSP plants have a reduced capacity factor and difficulties to supply electricity on demand to the grid. The integration of energy back-up systems may contribute to increasing power generation capacity and stability. Several options are being developed at present which are based on the incorporation of Thermal Energy Storage (TES) and also the use of auxiliary fuels. HYSOL is a new concept in CSP technology that relies on the integration of a molten salt TES system operating in hybrid mode with a biogas turbine with a Heat Recovery System (HRS). This paper illustrates the methodology and first results obtained during the development of the static model, considering a Base Case of HYSOL configuration. The study of this Base Case allows evaluating the impact of HYSOL technology, providing preliminary plant information and defining the required tools to be used in the project

Life Cycle Assessment of bamboo (guadua angustifolia stems) as building material for structural applications

Bamboo products have been proven to be a good altemative to hardwoods in the production of building materials, thus reducing the risk of deforestation primarily in tropical areas. Furthermore, bamboo also benefits from a very fast growing capacity when cultivated under adequate conditions, the ability to grow in non-productive land (e.g. eroded slopes) and the capacity to resprout from its stump due to its resilient root structure. Furthennore, its extensive root network promotes carbon sequestration, facilitates protection against soil erosion and reduces water depletion. Besides, from a social and economic point of view, cultivation and comercial utilization of bamboo materials support local economies in rural areas of developing countries. Bamboo stems have excellent mechanical properties that allow its use as supporting structures replacing conventional construction materials such as hardwood, steel or precast concrete. The environmental benefits of usi ng this material need to be quantified. This paper investigates greenhouse gas (GHG) emissions and energy performance of bamboo stems (guadua angustifolia) produced in Colombia under semi industrial conditions and utilized in Spain. These sustainability indicators are obtained using Life Cycle Assessment (LCA) methodology considering the following stages: stem harvesting in sustainably managed plantations, transport to processing plant, preservation/drying, transport to harbor, transport from harbor to harbor (from Colombia to Spain), transport to warehouse and storage. The functional unit considered in this assessment is a 6 meter-long stem, and the scenarios anal yzed include steam diameters 6, lO and 12 cm (weighing 1O, 14 and 17 kg respectively, dry matter basis). The calculations have been performed using Simapro 8 software and applying LCI databases from Ecoinvent v3 and ELCD v3. The environmental impacts associated with the consumption of electricity throughout the production, harvesting, processing and transportation of the bamboo materials have been adapted to the electricity mix in Colombia