Rock Storage Research Articles

Method for estimating methane emissions from Polish coal mining

Abstract To improve the accuracy of estimations of methane emissions from coal mining, a study of the Polish mine-specific method of methane measurement has been undertaken. To carry out the study, the following assumptions have been made: (1) Methane emissions are proportional to the gas content of coals; (2) The single mine average gas content is a function of both exploitation depth and gas distribution; (3) The total volume of methane released during mining is in proportion to the total gas content, while the volume emitted from post-mining processes and from waste rock storage to the residual gas content. The study has shown that: (1) There are four sources of methane emission from coal mining: mining and post-mining processes, degassing systems and barren rocks storage; (2) Emission from degassing systems should be measured directly, while the emissions from the other sources could be estimated and characterized by release factors; (3) The release factors for mining processes are described by parabolic equations, which have been defined by comparing total measured emissions from venting and degasing systems with in-situ methane content. For the remaining emission sources the factors are equal either to the average residual gas content or to the total gas content, depending on the proportion of residual to the total gas content; (4) Release factors and emissions, calculated for Polish coal mining were found to be four times less than had been previously suggested.

96/04043 A zomeworks retrospective

This article discusses practical design and manufacture of mostly passive solar energy equipment and systems. Included are the following topics: passive air loop rock storage systems for heating houses; moveable insulation; natural nighttime cooling use; solar water heaters.

An Integrated Approach to an Energy Efficient House

An energy efficient house has been built in Tasmania. It uses nearly 80% less conventional energy than an average house in the region. The intention of the designer was to demonstrate that if such a house could operate successfully in the coldest state of Australia, similar or even better results could be achieved in other temperate regions of the country. Active solar heating in combination with a heavily insulated light weight building envelope is the main feature of this integrated design for energy efficiency. The house, simple in construction, has been designed to operate effectively, a) without heat storage, while maintaining thermally comfortable indoor conditions and b) with heat (rock) storage and solar preheating of water in future, which will further reduce conventional energy use. Particularly evident in the design is the direct problem solving approach and innovative use of presently available technology.

Analyses of gas storage capacity in unlined rock caverns

Groundwater control is a means of ensuring that no gas leakage occurs from unlined rock storage caverns. To achieve a better understanding of the principles of gas containment under groundwater and how to obtain maximum gas storage capacity, analyses of groundwater conditions surrounding storage caverns and the effects of different factors on gas storage capacity have been performed and are reported in this paper. The analysis results indicate that the critical gas pressure of a storage facility is considerably less than the natural hydrostatic pressure around the caverns and somewhat less than the water curtain pressure. High gas storage capacity can be obtained by optimizing the design of cavern configuration, water curtain layout, cavern depth, etc. The principles of such optimization are outlined in this paper.

Basic consideration on storage of compressed natural gas in rock chambers

Compressed gas energy storage (CGES) works with gas in the gas phase and not in the liquid phase, thus avoiding the necessity of temperatures below 0° C. The paper discusses fundamental aspects of the two possible concepts of gas storage in rock: in lined and unlined chambers. Emphasis is placed on the rock engineering problems associated with the design of such schemes. It becomes clear, however, that the thermodynamic background, the operational aspects and safety concerns strongly interact with rock mechanics considerations.

Submerged geo-spacing for compressed air energy storage in deep soft rock. Provisional study of feasibility relating to urban siting in future : Hayashi, M Proc International Conference on Storage of Gases in Rock Caverns, Trondheim, 26–28 June 1989P377–387. Publ Rotterdam: A A Balkema, 1989

Submerged geo-spacing for compressed air energy storage in deep soft rock. Provisional study of feasibility relating to urban siting in future : Hayashi, M Proc International Conference on Storage of Gases in Rock Caverns, Trondheim, 26–28 June 1989P377–387. Publ Rotterdam: A A Balkema, 1989

Design and construction of a LPG rock cavern near by an existing LPG rock storage : Palmqvist, K; Ullgren, S Proc International Conference on Storage of Gases in Rock Caverns, Trondheim, 26–28 June 1989P307–315. Publ Rotterdam: A A Balkema, 1989

Design and construction of a LPG rock cavern near by an existing LPG rock storage : Palmqvist, K; Ullgren, S Proc International Conference on Storage of Gases in Rock Caverns, Trondheim, 26–28 June 1989P307–315. Publ Rotterdam: A A Balkema, 1989

Design and development of an augmented integrated solar collector with rock storage system for heating applications

The main objective of this research communication is to furnish the necessary information to correctly design a solar air heating system that can be used for residential or agricultural applications. An inexpensive augmented integrated solar collector cum storage system using rocks as a sensible heat storage medium has been designed and fabricated to provide low grade heat to suit the needs for space heating and agricultural applications. Experimental observations of fluid temperature, energy storage and other measures of system performance are also presented in detail.

The effects of bale density, type of binding and storage surface on the chemical composition, nutrient recovery and digestibility of large round hay bales

Alfalfa-bromegrass forage was cut at midbloom, sun cured to 847 g dry matter (DM) kg −1 and baled as either high-density (189 kg m −3) or low-density (146 kg m −3) large round bales bound with either plastic mesh (2 cm between strands) or sisal twine spaced at 15 to 20 cm. Bales were stored outside either on a 15 cm layer of crushed rock (7.5 cm diameter) or on the ground. High-density bales had higher ( P < 0.01) mean temperatures during the first 32 days of storage than low-density bales. After 4 and 9 months of storage, high-density bales had a higher ( P < 0.05) DM concentration and a lower ( P < 0.01) proportion of N as acid detergent insoluble N (ADIN) than low-density bales; these effects were greatest in the outer 30 cm of the bales (density × part, P < 0.05). High-density bales had a greater ( P < 0.01) unweathered DM recovery than low-density bales. Plastic mesh-bound bales had: higher (binding × part, P < 0.01) in vitro digestible dry matter (IVDDM) concentrations, lower neutral detergent fiber (NDF; binding × part, P < 0.01), acid detergent fiber (ADF; binding × part, P < 0.01), acid detergent lignin (ADL; binding × part, P < 0.05) and ADIN (binding × part, P < 0.01) concentrations in their outer 30 cm and greater ( P < 0.01) recoveries of total DM, unweathered DM and IVDDM than twine-bound bales after 4 and 9 months of storage. Plastic mesh binding resulted in: smaller (density × binding, P < 0.01) increases in ADF, ADL and ADIN concentrations and smaller (density × binding, P < 0.05) decreases in total DM, unweathered DM and IVDDM recoveries in low-density than in high-density bales. Bales stored on crushed rock had lower ( P < 0.01) temperatures during the first 32 days than ground-stored bales. After 4 and 9 months of storage, rock-stored bales had higher ( P < 0.01) DM concentrations than ground-stored bales; this effect was greater in hay from the outer 30 cm of the bales (surface × part, P < 0.01). Bales stored on crushed rock had higher (surface × part, P < 0.01) IVDDM concentrations in their outer 30 cm and greater unweathered DM ( P < 0.01) and IVDDM ( P < 0.05) recoveries than ground-stored bales. In digestion trials, plastic mesh binding or rock storage of high- or low-density bales resulted in greater ( P < 0.05) DM intakes by sheep than twine binding or ground storage, but had no effects on hay DM digestibility.

Two-phase boundary layer formation in a semi-infinite porous slab

Similarity profiles of pressure and saturation are analysed which result from one-dimensional planar withdrawal of fluid from a porous region initially containing a two phase mixture of steam and water. Approximate expressions are derived for the evolution of pressure and saturation profiles, and boundary-layer changes in saturation are identified. The existence of a similarity variable implies that the saturation conditions for the reservoir tend with time either to having both phases flowing; or to a single phase vapour. In particular, the nonlinear nature of the governing equations implies that infinitesimal changes in pressure can produce finite changes in saturation. The two mechanisms responsible for saturation changing with time involve local changes in energy storage in rock and fluid; together with spatial variations in flowing enthalpy. The latter mechanism occurred relatively slowly in the examples treated, and was responsible for boundary-layer formation when one phase was initially immobile. Dimensional analysis reveals that when a boundary layer develops, the underlying equations involve essentially only one dimensionless parameter which is typically small, being associated with the ratio of the energy density of the mobile phase relative to the total energy density.

A summary of operation results for the air solar heating system for Module 6 of the Alberta Home Heating Research Facility

The air solar heating system installed in Module 6 at the Alberta Home Heating Facility has an 11-m 2 double-glazed, south-facing solar collector tilted at 68°, a 2-m 3 rock storage unit, one air handling unit, motorized dampers, a two-stage electric furnace, and a system controller. The performance of the system was calculated by comparing the difference in electric power required for Module 6 and Module 5, a module of similar construction, and using the measured solar energy collected and the electric power required by Module 6. The monthly solar fraction ranged from 0 to 70%. The dynamic behavior of the solar collector was also studied.

Large scale seasonal heat storage in rock : Nordell, B Proc International Symposium on Engineering in Complex Rock Formations, Beijing, 3–7 November, 1986P351–356. Publ Beijing: Science Press, 1986

Large scale seasonal heat storage in rock : Nordell, B Proc International Symposium on Engineering in Complex Rock Formations, Beijing, 3–7 November, 1986P351–356. Publ Beijing: Science Press, 1986

Fracturing of a pilot plant for borehole heat storage in rock

This paper describes research on a pilot plant in Luleå, Sweden. The plant consists of 19 boreholes, 52 mm in diameter, for heat supply and extraction; and 10 boreholes for temperature monitoring. All the boreholes are 21 m deep. The report describes in detail the performance and results of rock mass permeability and borehole permeability tests. It also discusses hydraulic fracturing and explosive fracturing in the boreholes. A simulation model of water flow in the test plant is described. The paper includes conclusions from the test results and recommendations for further study. Cet article décrit la recherche effectuée pour une usine pilote à Luleå (Suède). L'usine comprend 19 forages de 52 mm de diamètre, utilisés à la fois pour les circuits de chauffage et l'extraction; ainsi que 10 forages permettant la surveillance de la température. Tous ont 21 mt̀res de profondeur. Le rapport décrit en détail les performances et les résultats d'essais de perméabilité des forages et des roches. Il traite aussi de la fracturation hydraulique ou par explosion des forages. Un modèle de simulation des écoulements d'eau dans cette usine pilote est présenté. Sont aussi inclues les conclusions des résultats et des essais, ainsi que des recommandations pour des études ultérieures.

Transient response of latent heat storage in greenhouse solar system

A latent heat storage system with two different stacking configurations and air bafflings was designed and constructed as an integrated part of the greenhouse solar system (solar barn). Commercial cylindrical storage rods were used as the primary storage elements. The results showed that the designed latent storage systems demonstrated significantly higher compact storage capacity than water or rock storage and that the ring-baffled storage unit performed better than the cross-baffled storage unit.

Performance analysis of a solar air-conditioned villa in the arabian gulf

An integrated system which utilizes three types of solar energy subsystems for the purpose of air-conditioning (i.e. heating and cooling) in residential buildings has been designed, installed and tested in the KISR solar house, Kuwait. The three systems are: (a) a solar photovoltaic power system, (b) a solar air heating and rock storage system and (c) a solar water heating, cooling and domestic water heating system. This paper gives a general survey of the design and operation of the solar energy systems. The performance of the different solar energy systems is reported in terms of collector efficiency, solar energy contribution and the use of electrical energy to operate the solar equipment and of fossil fuels to back up the operation of the solar energy system. The general characteristics of the three types of systems are also compared. Information concerning installation, operation and maintenance of the systems has been discussed.

A numerical model for seasonal storage of solar heat in the ground by vertical pipes

We present a three-dimensional numerical model for seasonal heat storage in the ground using vertical heat exchanger pipes. The model also accounts for convective heat flows in the ground. The storage is employed in a district solar heating system with a heat pump. The effects of storage volume, storage medium, collector area, and collector type on system performances are studied for the Helsinki (60°N) climate. Economic optimization of the storage and collector installation is also briefly discussed. For a 500-house community, a collector area of 35 m 2 per house and a rock storage volume of 550 m 3 per house would provide a solar fraction of 70%.

Performance studies of a double glazed augmented integrated rock system

This paper describes the design details of and experimental investigations on a prototype augmented integrated rock system (AIRS) with an intention of using solar energy for crop drying and space heating. The system investigated is a flat plate solar collector of conventional design connected in series with rock storage and a collection unit. For the evaluation of the 24 hour performance of this system, outdoor calorimetric tests have been performed. The experimental results for varying inlet air flow rate have been analysed and the final results have been included. AIRS' overall daily efficiency is determined by testing the system outdoors and monitoring the output energy and the incident solar radiation. Taking into consideration the total cost of the system it has been designed so that it can be fabricated on site using, wherever possible, readily available tools and materials.

Some mechanical aspects of low cost augmented integrated rock system

The development of an augmented integrated rock system is described in this paper. A unique AIRS (Flat Plate air heater connected in series with an integrated rock storage and collection system) concept is used as the absorber plate-to-air stream and then air stream-to-rock bed storage and collection unit heat transfer mechanism. The intention was to increase the efficiency of the air heater, over that of a ‘conventional’ type solar air heater by increasing the absorber area which includes the metallic absorber plate and the rock surface exposed directly to the sun. The programme objective was to design a device which can store the energy during its operation and supply it during the evening and late night hours when there is no sun in the sky. In order to achieve this goal, we have fabricated, tested and evaluated ‘AIRS’, and the results obtained are presented in this paper.

Radon and radon daughter measurements in solar buildings.

Measurements of radon and radon daughters in 11 buildings in five states, using active or passive solar heating, showed no significant excess in concentrations over the levels measured in buildings with conventional heating systems. Radon levels in two buildings using rock storage in their active solar systems exceeded the U.S. Nuclear Regulatory Commission's limit of 3 pCi/l. for continuous exposure in uncontrolled areas. In the remainder of the buildings, radon concentrations were found to be at levels considered to be normal. It appears that the slightly elevated indoor radon concentrations result from the local geological formations and from the tightening of the buildings rather than as a result of the solar heating technology.

Exchanged air control for maximum solar energy utilization in tobacco curing

ABSTRACT TOBACCO was cured in three one-fifth scale (30 rack) units loaded on a MWF schedule each week for four weeks. A single-glazed flat plate collector and rock storage system raised the ambient temperature an average of 24.5 C during the day and 20.2 C at night to supply 37 percent of the required heat energy. The mean supplemental heat requirement was 12.7 MJ/kg of cured tobacco solids. Expressions for each term in an energy balance model are presented, and evaluated hourly in a simulation. Error in closure of the energy balance ranged for -6.8 percent to -0.1 percent with a mean of -3 per-cent for the 12 cures. The exchanged air rate was increased during the day to maximize usage of the solar system. The energy balance model was used to compare this strategy with a constant ventilation rate for each day du-ing the cure, equal to the time average rate for that period measured during the experiments. Increasing the rate during the day resulted in a 2 to 10 percent increase in the solar contribution with a mean of 5 percent for the 12 cures. Actual cure energy for the exchanged air schedules ranged from 21 to 37 percent more than the theoretical minimum calculated with the energy balance model. As a general guideline, the exchanged air schedule should be 20, 35, 50, 70, 40, and 20 air changed per hour for days 1 through 6 respectively. For a 5-day cure a general guideline is 30, 30, 50, 40, and 25 air changes per hour.