Operation of a 25 KWth Calcium Looping Pilot-plant with High Oxygen Concentrations in the Calciner

Summary

This manuscript describes a procedure for operating a calcium looping pilot-plant for post-combustion carbon capture with high oxygen concentrations in the calciner in order to reduce or eliminate the flue gas recycle.

Abstract

Calcium looping (CaL) is a post-combustion CO₂ capture technology that is suitable for retrofitting existing power plants. The CaL process uses limestone as a cheap and readily available CO₂ sorbent. While the technology has been widely studied, there are a few available options that could be applied to make it more economically viable. One of these is to increase the oxygen concentration in the calciner to reduce or eliminate the amount of recycled gas (CO₂, H₂O and impurities); therefore, decreasing or removing the energy necessary to heat the recycled gas stream. Moreover, there is a resulting increase in the energy input due to the change in the combustion intensity; this energy is used to enable the endothermic calcination reaction to occur in the absence of recycled flue gases. This paper presents the operation and first results of a CaL pilot plant with 100% oxygen combustion of natural gas in the calciner. The gas coming into the carbonator was a simulated flue gas from a coal-fired power plant or cement industry. Several limestone particle size distributions are also tested to further explore the effect of this parameter on the overall performance of this operating mode. The configuration of the reactor system, the operating procedures, and the results are described in detail in this paper. The reactor showed good hydrodynamic stability and stable CO₂ capture, with capture efficiencies of up to 70% with a gas mixture simulating the flue gas of a coal-fired power plant.

Introduction

CO₂ emissions and the resulting global warming are critical environmental issues that have attracted a large amount of research in the past years. Carbon capture and storage (CCS) has been acknowledged as a potential technology for reducing CO₂ emissions to the atmosphere^1,2. The most challenging part of the CCS chain is the capture of CO₂, which is also the most costly stage³. In consequence, there has been a focus on developing new technologies for CO₂ capture from power plants and other industrial facilities.

CaL....

Protocol

1. Material Preparation

1. Sieve the limestone (~50 kg of raw material) to the desired particle size distribution (300-400 µm or another distribution depending on the experiment) using a mechanical shaker. Put the sieved material in pots next to the calciner for feeding during the test.
2. Prepare the material in batches to be introduced into the reactor. The batches are generally 0.5 L or 1 L (1 L of limestone is roughly 1.5 kg), but this can vary depending on the operating parameters.

2. Start-up Procedure

CAUTION: Extremely high temperatures are achieved here. Suitable PPE such as gloves, ....

Results

The experimental set-up is shown in Figure 3. The plant comprises two interconnected fluidized-beds. Namely, the carbonator is a CFB with 4.3 m height and 0.1 m internal diameter (ID); while the calciner is a BFB with 1.2 m height and 0.165 m ID. The solid transport from one reactor to the other is controlled by two loop-seals fluidized with nitrogen. Both reactors are fed a mixture of gas through a preheating line, and both are electrically heated; moreover,.......

Discussion

The operation of the calciner with an inlet of 100% vol oxygen is achievable, based on exploiting the endothermic nature of the calcination reaction, as well as the fact that the solids circulate between the two reactors at different temperatures. This operating mode aims to make the CaL process more economically promising by reducing capital and operating costs. As the recycle of flue gas (mainly CO₂, water vapor and unreacted O₂) is reduced or even eliminated, the heat consumed to preheat this str.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Longcal limestone	Loncliffe	Longcal SP52	n/a
Mechanical Shaker	SWECO	LS24S544+C	Mechanical siever to separate particles
Oxygen	BOC	n/a	BOC cylinders
Nitrogen	BOC	n/a	BOC tank
Carbon dioxide	BOC	n/a	BOC tank
Natural gas	n/a	n/a	Taken from the line